Introduction to On Board Diagnostics (II)

Introduction to On BoardDiagnostics (II)On board Diagnostics Regulations in the U.S.A. forlight and medium duty vehicles (internal combustion engines)are introduced to implement the air quality standards.In this respect California Motor vehicle PollutionControl Board (CMVOCB) was created in 1960.California and the federal government used adriving cycle to certify 1966 vehicles and newermodels which was referred to as either CaliforniaCycle or the Federal Test Procedure (FTP)The following OBD II requirements are in force:All vehicle’s emission control systems and components that can affect aemissions must bemonitored. Malfunctions must be detected before emissions exceed 1.5 times the standardspecified by EPA.Malfunctions must be detected within 2 driving cycles.If a malfunction is detected a Malfunction Indicator Light (MIL) is illuminated.

Introduction to On BoardDiagnostics (II)The First major Clean Air Act was adopted by the Congress in1970.Congress established the Environmental Protection Agency(EPA) with the overall responsibility of regulating motorvehicle pollution to the atmosphere. Congress also identifiedthe Inspection and Maintenance (I/M) programs as analternative for improving the air quality.

Introduction to On BoardDiagnostics (II)All of the previous regulations led to the appearance of thecharcoal canister, exhaust gas recirculation (EGR) valves, andfinally the catalytic converters in 1975.Moreover, in 1977 amendments to the Clean Air Act mandatedinspection and maintenance for vehicles used in high-pollution areas affected by high Hydro carbon (HC) emissions.

Introduction to On BoardDiagnostics (II)On Board Diagnostics (OBD) systems were designed tomaintain low-emissions of in-use vehicles, includinglight and medium duty vehicles.In 1989, The California Code of Regulations (CCR) known asOBD II was adopted by the California Air Resources Board(CARB)OBD II is the next generation OBD system of vehiclesdesigned to reduce the time between occurrence of themalfunction and its detection and repair, with the objectiveto reduce hydrocarbon (HC) emissions caused bymalfunction of the vehicle’s emission control system.

Introduction to On BoardDiagnostics (II)OBD II system is designed to satisfy EPA regulations whichlimit the amount of HC emissions from the vehicle.OBD II will also minimize the damage to other vehiclesystems or components.Such diagnostic systems are implemented by incorporatingadditional software and hardware in the vehicle electronicssystem to collect and analyze data already available to theon-board computer, and monitoring the entire emission controlsystem.

Introduction to On BoardDiagnostics (II)The U.S. Federal Government has published test procedures that include iseveral steps such as Dynamometer test, Hydro Carbons Analyzer, and otherAnalyzers. The vehicle is operated according to a prescribed schedule of speed and loadto simulate highway driving as well city driving. The emissions are then measured usingthe above instruments. Standards have been set for the vehicle half-life life (5 years or 50000miles which ever comes first) and full cycle (10 years or 100000 miles). The followingstandards are enforced 100% after 1996:• HC 0.31 gms /mile• CO 4.20 gms/mile• NOx 0.60 gms/mile (non-diesel)• 1.25 gms/mile (diesel)

Introduction to On BoardDiagnostics (II)These FTP regulations are enforced by EPA for all Light andMedium Duty vehicles made in U.S.A. The standards forEuropean and Asian made vehicles have different standardswhich are more relaxed.The European and Asean standards are not yet completelyfinalized by their countries.

Introduction to On BoardDiagnostics (II)OBD II requires the manufacturers to implement new comprehensiveon-board diagnostic systems beginning in the 1994 model year,to replace OBD IThe EPA in 1978 issued its first policy for Inspection andMaintenance (I/M) of vehicles that emitted Hydro Carbons intothe atmosphere.As emissions increased, the EPA regulations grew stricter, resultingin the introduction of the 3-way 3catalytic converter, on-board computersand oxygen sensors in 1981.

OBD II monitors more components and systemsthan OBD-I, including:• Catalytic converters• Evaporative control System• Emissions control system• Emissions related powertrain performance - Oxygen sensor• Emissions related sensors and actuators- EGR monitoring• Detection of engine misfire• PCV (Positive Crankcase Ventilation) (implementation: 2002 - 2004)• Fuel system - closed loop fueling performance• Thermostats (implementation: 2000 - 2002)Components are monitored for :uCircuit continuity and out of range values of sensors, actuators, , switches, and wiresuFunctional checks for output components listed aboveuReasonable value checks during vehicle operation such as rationality, sanity, or logic checks forinput components, and output components where applicable.Thermostat monitoring is the new addition to the existing OBD II requirements. This isrequired due to:uThermostat degradation can extend the time of open-loop operation at start-upuProlonged open-loop operation will increase emissionsu“warmed-up” coolant temperature is a must for all OBD II monitoring operations.New requirements for thermostats for 2000-2002 2002 implementation include the following:uDetection of malfunctions that will affect the coolant temperature re and disable OBD II monitoring functions due to lower thannormal temperature operation of the vehicleuDetection of malfunctions that will prevent vehicle from reaching g normal operating temperature.PCV (Positive Crankcase Ventilation) failure will increase the emissions eby 1.2 g/mi for Hydro Carbons per vehiclePCV must be monitored for this reason and its requirements are:Detect PCV hose disconnections that can cause increased emissionsMeet all design guidelines concerning hoses and valve connections s and materials to ensurepositive crankcase ventilation.

Introduction to On BoardDiagnostics (II)The intent of OBD II systems is to detect most vehiclemalfunctions when performance of a powertrain component orsystem deteriorates to the point thatthe vehicle’s HC emissions exceed the thresholdvalue tied to the applicable EPA emission standard.The vehicle operator is notified at the time when the vehiclebegins to marginally exceed emission standards, byilluminating the Malfunction Indicator Light (MIL)

Introduction to On BoardDiagnostics (II)Both CARB and EPA regulations require monitoring of systems, and illuminatingMIL and storage of a Diagnostic Trouble Code (DTC) if a fault is detected.Once per trip evaluation:uCatalyst Catalyst efficiency (conversion efficiency)uHeated Heated catalyst (time to attain rated temperature)uEvaporative system (air flow /vapor leak detection)uSecondary Air system (proper air amount during idle)uOxygen Oxygen sensor (output voltage and response frequency)uOxygen Oxygen sensor heater (proper current and voltage drop)uEGR EGR system (proper exhaust gas flow rate into intake manifold)

Introduction to On BoardDiagnostics (II)Continuous evaluation:uMisfire detection (percent misfire and specific cylindernumber)uFuel system performance (proper fuel delivery and nozzleflow)uComprehensive component monitoring - Input sensor andoutput actuator that can affect emissions.uincrease in emissions greater than 50 % of standard isconsidered objectionable.

Introduction to On BoardDiagnostics (II)OBD II is an onboard diagnostics and service methodology.OBD II mandates a standard scan tool (SAE J 1978) with a single standardplug for all vehicles manufactured in U.S.A.Diagnostic test modes (SAE J 1979) include:uFault Fault code handlingu“Readiness” codesuReal Real time vehicle informationu“Freeze “Freeze Frame” information.Standard nomenclature for all OBD II codes (SAE J 1930) is mandated.OBD II standardizes on most Trouble Codes (TC) for vehiclemalfunctions identified by regions, such as powertrain, , body, etc.OBD II standardizes on number of sensor readings, messageformats, message priorities, etc. for all vehicles.

Introduction to On BoardDiagnostics (II)OBD II standardizes on the amount of memory (“FreezeFrame”) it uses to store the readings of the vehicle sensors whenit logs an emission related intermittent (“history”) TroubleCode(TC).OBD II standardizes on diagnostic method of storing troublecodes and displaying Malfunction Indicator Light (MIL) whichcannot be removed until the malfunction is repaired.

Introduction to On BoardDiagnostics (II)OBD II provides additional information to technician for diagnosis is and repairof emission related problems.Item Legal Requirement Diagnostic techniquet______________________________________________________Catalytic Converter Illuminate MILDual sensors placedmonitoring when HC conversion efficiencyat the front and rear end of thefalls to 60%converter___________________________________________________________________________Misfire monitoring Illuminate MIL on detectingMeasure change inmisfires in predefined % of crankshaft speedmisfires in any cylinder(s) and estimate indicatedwithin 200 or 1000 revolutions torque developed bydepending on cold starteach cylinder after(open-loop) orcombustion.closed-loop loop operation.Complicated computationsare carried out. Also identify ithe specific cylinder experiencingmisfire._______________________________________________________________________________

Introduction to On BoardDiagnostics (II)_______________________________________________________________________________Fuel System Illuminate MIL when deviations, ofMeasuredeviations of fuel demandmonitoringstoichiometric ratio which last for a fromstoichiometric ratio overlonger time stored within adaptive prolongedamount of time. Comparemixture controller, exceed defined value of Lambdasensor with O 2 sensorlimits due to fuel systemcomponents not complyingwith specification._______________________________________________________________________________

________________________________________________________________________________Oxygen sensor Illuminate MIL when the switchingMonitor response time of two lambdamonitoring frequency of the control-loop loop exceeds sensors in front and rear of thepredefined limit. Check input t circuit catalytic converter. Lambda sensorvoltage for detecting short circuit reacts slower on variations of the A/For open circuit. Bias is 0.450 0 volts. mixture, thus increasing the period ofthe lambda sensor regulation whichis the inverse of the closed-looploopfrequency.____________________________________________________________________________________EGR monitoring Illuminate MIL when EGR operation Monitor manifold temperature change,fails to indicate increasemanifold pressure change, on EGR flow w andin Manifold pressure orengine RPM change as well. Use sensorsfails to indicate increase in to detect these changes.manifold intake temperature or .decrease of about 50 engine RPM.EGR can be intrusively induced d duringnormal operation, or interruptedtedwhen EGR operation is occurring andmonitor these changes.___________________________________________________________________________Secondary Air Illuminate MIL when lambda sensorMonitor lambda sensor reading whensystem monitoring deviation does not correlate withsecondary air is introduced into thesecondary air flow changes. . exhaust manifold or catalyticIn open-loop operation, the air flow converter’s second chamber.should be into exhaust manifoldprovided manifold temperature is_______________________________________________________________________________below threshold and engine load isbelow threshold. In closed-looploopoperation the air flow should beinto catalytic converter’s s secondchamber in three-way catalytic converter.

Introduction to On BoardDiagnostics (II)Most components are monitored, including the catalyst andevaporative system, such that a malfunction is signaled as theemissions exceed 1.5 time the applicable standards.OBD II requires the detection of relatively low rates of enginemisfire, to prevent serious damage to the catalytic converter .

Introduction to On BoardDiagnostics (II)Further, OBD II also includes “Freeze Frame”, which allows thecomputer to store in memory the exact operating conditionswhen a fault occurred, so intermittent faults can be investigatedby revisiting the same conditions when the problem occurred.A standard access electrical connector which is identical for allvehicles is required, which means that a single inexpensivegeneric tool can be used to read out fault codes.

Introduction to On BoardDiagnostics (II)Although OBD II requirements reflect state-ofof-the-art diagnosticsystem capability, there are limitations which apply to thecurrent techniques for detecting malfunctioning components.These limitations do not allow OBD II systems to take the placeof the FTP test for measuring vehicle emissions.The reason is that monitoring systems can detect whencomponents are functioning within their operating range, butare limited with the ability to determine whether they arefunctioning accurately within the range.

Introduction to On BoardDiagnostics (II)OBD II is associated with IM240, the enhanced inspection/maintenanceanceprogram for states with air quality program like California.IM240 also gets into the area of the new ASE (AutomotiveService Engineering) tests for the “super mechanics.”OBD II rules are copied from the CARB rules until 1997.OBD II rules for 1998 will be taken from EPA’s standards which includeiamong other things, an onboard computer to predict when a vehiclewill fail an emission test.

Introduction to On BoardDiagnostics (II)OBD II standardizes that many trouble codes which are set whena malfunction is detected in the emission related component of the tvehicle will be stored in computer memory without a prospectfor erasure prior to repair.OBD II mandates that all trouble codes are logged when theyare set and are retrieved by the scan tool when commanded.OBD II however turns on the Malfunction Indictor Light (MIL)selectively in malfunction situations that require immediateattention of the driver for safety reasons.

Introduction to On BoardDiagnostics (II)Specific “Freeze Frame” diagnostic data must be stored whenthe first malfunction is detected. If a second malfunction in thefuel system or misfire function occurs, then the first data mustbe replaced with the subsequent malfunction data. Diagnosticdata must be made available when requested by the Scan tool.Results of the most recent tests and limits to which those resultsare compared with, must be made available for all emissioncontrol systems, for which OBD II diagnostics are conducted.The message content and down loading protocol is defined forall fault codes, specific data values, and “Freeze Frame” data.

Introduction to On BoardDiagnostics (II)Malfunction must be detected before emissions exceed a specified threshold(generally 1.5 times the standards). In most cases, malfunctions must bedetected and logged within two (2) driving Cycles (California Cycles) ortrips.R & D(research and development) activity in monitoring malfunctions ofvehicle components such as catalytic converters continues at a very rapidpace.There is plenty of room for the application of advanced control and signalprocessing techniques to control vehicle exhaust emissions using g OBD II.

Powertrain and EmissionControls in PassengerVehiclesAn Overview:On-line diagnosis of internal combustion engines in passenger vehiclesis mandated due to the strict environmental regulations in the U.S.A Uand in some European countries (e.g.., the EFTA (European Free TradeTAgency) partners) to control Hydro carbon emissions from the exhaust.Powertrain subsystem consists of the engine and transmission including theexhaust emission control apparatus which needs to be continuouslymonitored by the engine controller (computer) for potential defectsleading to decreased effectiveness in emission control system (e.g., three-waycatalyst) resulting in increased emission of hydrocarbons which are regulatedby the EPA.

Powertrain and EmissionControls in PassengerVehicles (contd(contd)The powertrain components relevant to emissions are:• Throttle & Manifold• Exhaust & Fuel system• Combustion & Rotational dynamics• Automatic TransmissionEach of the above components is further divided into the following sub-components:Throttle & manifold:• Throttle Body assembly• Idle Air Control Valve (IACV)• Exhaust Gas Recirculation (EGR)• Intake Manifold

Powertrain and EmissionControls in PassengerVehicles (contd(contd)Exhaust & Fuel system consists of the following components:Exhaust & Fuel system:• Exhaust valves• Exhaust Gas line• Fuel Pump• Fuel Level Sensor• Vacuum Sensor• Canister Vent• Fuel Feed and Metering• Fuel Injection nozzles• Oxygen sensor• Catalytic Converter

Powertrain and EmissionControls in PassengerVehicles (contd(contd)Combustion and Rotational dynamics consist of the following components:onents:Combustion and Rotational dynamics:• Engine• Crankshaft assembly and flywheel• Crank angle sensor• Mass Air Flow (MAF) sensor• Coolant Temperature sensor• Manifold Absolute Pressure (MAP) sensor• Engine Speed sensor• Knock sensor• purge solenoid

Powertrain and EmissionControls in PassengerVehicles (contd(contd)Automatic transmission consists of the following components:Automatic Transmission:• Torque Converter• Automatic transmission input shaft• Transmission lockup clutch• Hydraulic pump and hydraulic circuit• Solenoid valves• Throttle Position sensor• Vehicle Speed sensor• Transmission input shaft speed sensor

Powertrain and EmissionControls in PassengerVehicles (contd(contd)The goal of the On-Board Diagnostics is to alert the driver to the presence ofa malfunction of the emission control system , and to identify the tlocation ofthe problem in order to assist mechanics in properly performing repairs. Inaddition, the OBD II system should illuminate the Malfunction IndicatorLight (MIL) and store the Trouble Code in the computer memory for r allmalfunctions that will contribute to increased HC emissions.The Powertrain is controlled by the Powertrain control module (PCM)computer to deliver the required torque to the vehicle requested by thedriver and to limit the vehicle emissions to the required minimum m to meetEPA regulations.

Powertrain and EmissionControls in PassengerVehicles (contd(contd)The powertrain functions are described to show how the PCM controls the emissions while delivering thetorque to the vehicle requested by the driver.Throttle & Intake Manifold: The Throttle Body assembly is an air valve. It regulates the air flow into theengine and thereby contributes to the control of engine speed and d power. IACV(idle air control valve )provides additional air flow during starting of the engine and during idle.IACV bypasses the throttle to provide additional air to compensate for the loads during closedthrottle. EGR (exhaust gas recirculation)provides exhaust gases to the intake manifold. This has the effect ofreducing oxygen content in the enginecylinder. This in turn reduces the combustion temperature of the cylinder flame. This has theimportant effect of reducing the NOx (Oxides of nitrogen) emissions which is regulated by the EPA.Intake manifold is the main air passage from the throttle valve to the engine cylinders. The amountof air through the intake manifold to the cylinder is the same for feach cylinder on each intake stroke.Then each cylinder requires an amount of fuel determined by the density of the air in the cylinder.MAP sensor is used to compute the density of the air in the intake manifold. Barometric absolutepressure is used to compute the EGR flow. The Manifold vacuum is the difference between thesetwo pressures which is measured. The required fuel is in direct proportion to this air mass whichis controlled by the PCM to maintain the exact stoichiometric ratio (14.7) of air/fuel that gives theminimum HC emissions and meet EPA regulations.

Powertrain and EmissionControls in PassengerVehicles (contd(contd)Exhaust & Fuel system:Exhaust valves of the engine cylinders purge the exhaust through the Exhaust Gas linewhich then passes through the catalytic converters in which most of the HC and CO (carbonmonoxide) are oxidized to CO 2(Carbon dioxide) and water. The extra oxygen required for thisoxidation is supplied by adding air to the exhaust stream from an engine driven air pump. This aircalled secondary air, is normally introduced into the exhaust manifold. mThis has a considerableeffect in reducing emissions and meet EPA regulations.The Fuel Pump supplies metered fuel which is electronically injected through nozzles operatedby solenoids under control of the PCM. The fuel in the fuel tank is filtered.The Fuel Level Sensor measures the amount of fuel in the tank.The vacuum sensor measures the inlet vacuum which is a measure of fuel pump suction whichaffects pump priming. The inlet vacuum is monitored to ensure that inlet flow of the fuel to thecylinders is not restricted.

Powertrain and EmissionControl in Passenger Vehicles(contd)Canister vent & Fuel systemThe Canister Vent is used to direct fuel vapors out to a canister r where the vapors areabsorbed by active char coal in the canister. The purge of the fuel fvapors is donevia purge valve periodically.The Fuel Feed and Metering is performed, by the PCM, to match the e mass air flowwhich minimizes HC emissions. The air flow is controlled by the throttle valvewhich is operated by the driver’s pedal.The Fuel Injection nozzles inject the fuel as a spray that spreads the fuel into thecylinder in an atomized manner to mix with the air for complete combustion.

Oxygen sensor:Powertrain and EmissionControls in PassengerVehicles (contd(contd)The Oxygen sensor is used to monitor the residual oxygen (after catalysis in theconverter) in the exhaust gases. The oxygen sensor output is calibrated tomeasure the air/fuel ratio (which is proportional to oxygen in the texhaust gases)in the engine cylinders. This ratio, called Lambda, is one (1) for stoichiometric(14.7) air/fuel ratio. This is the target for realizing minimum emissions.The oxygen sensor is used as stoichiometry detector and is connected in a closedloop in a Limit Cycle control. The oxygen sensor output is a switch signal(ON/OFF) that brings back the A/F ratio to 1 when it varies between een 0.93 to 1.07.

Powertrain and EmissionControls in PassengerVehicles (contd(contd)Oxygen sensorThe reason that oxygen sensor behaves in this manner is thatthe catalytic converter is most efficient in eliminating allpollutants by oxidizing HC to CO 2 and reducing NOx to N 2when the exhaust gases indicate a stoichiometric (14.7) air/fuelratio, indicated by the Exhaust Gas Oxygen (EGO) Sensor..Catalytic Converter is a three way catalyst which will oxidizethe Hydro carbons including CO to CO 2 and reduce the NOx toN 2 in the exhaust gases simultaneously thus removingpollutants.

Combustion and Rotational dynamics: (Figures 1 to 3)The Engine provides the mechanical power to the vehicle. The engine cylinders perform the combustion of air/fuelmixture at stoichiometric ratio (14.7). The Crankshaft assembly and flywheel house the Crank angle sensor which sensesthe position of the Top Dead center (TDC) of the cylinder and provides the necessary ignition spark at the correct crankangle between the reference point on the flywheel and the horizontal centerline of crank shaft. The amount of fuel neededfor the combustion in the engine cylinder is a direct function of the throttle position and the mass of air through the intakemanifold which is controlled by the driver’s accelerator pedal. This mass of air is measured with the Mass Air Flow(MAF) sensor. The correct air mass is computed by compensating for fthe intake air temperature which is measured by theintake air temperature sensor. The Manifold Absolute Pressure (MAP) sensor measures the intake manifold pressurewhich is also used to measure the amount of air going into the cylinder as a second method to determine the amount offuel that should be sent to the fuel injection nozzles for spraying into the cylinder. This is to ensure that accurate amountof fuel is used in the cylinder to achieve fuel economy as well as to reduce emissions by efficient combustion. An EngineSpeed sensor is needed to provide an input to PCM to compute ignition timing. Engine speed is measured by enginespeed sensor similar to crankshaft position sensor. Another variable able which must be measured for engine control is thethrottle angle or the throttle valve position which is measured by the Throttle Angle Sensor.The throttle plate is mechanically linked to the accelerator pedal which is operated by the driver. When the pedal ispressed the throttle plate rotates and allows more air to pass through tthe intake manifold. The angle of rotation of throttleplate is measured by the throttle angle sensor. This can be used to measure the mass of air going into the cylinder.Knock is caused by a rapid rise in cylinder pressure during combustion caused by high manifold pressure (MAP) andexcessive spark advance. It is important to detect knock and avoid excessive knock to avoid damage to the engine. Knockis detected by the Knock sensor.During engine off condition, the fuel stored in the fuel system tends to evaporate intothe atmosphere. To reduce these HC emissions, they are collected by a charcoal filter in a canister.The collected fuel is released into the fuel intake through a purge solenoid valve controlled by thePCM periodically.

Powertrain and EmissionControls in PassengerVehicles (contd(contd)Automatic Transmission:The Automatic transmission uses a hydraulic or fluid coupling to transmit engine power to the wheels.Efficient transmission of engine output to the automatic transmission ssion input shaft is performed througha transmission lockup clutch similar to a standard pressure-plate plate clutch placed inside the torqueconverter (the fluid coupling used as a torque amplifier). In order to smoothly engage the lockup clutchthe hydraulic fluid pressure is adjusted by controlling the output current applied to the lockup solenoidvalves.Automatic transmission is controlled by inputs from the vehicle speed sensor and throttle position sensorwhich senses the vehicle load. The automatic gear shift points, the point at which the lockupclutch is activated, and the clutch’s hydraulic pressure level are acontrolled by the PCM. The optimalshifts and lockup operations are carried out using a solenoid valve to open and close the hydrauliccircuit, primed by the hydraulic pump.The transmission’s input- shaft speed is monitored during shifting by the speed sensor after the ON/OFFsignal is output from the shift solenoid valves. The shifting process pis adjusted by the hydraulic pressureof the clutch so that the clutch is smoothly engaged. The engine torque is controlled in synchronism withthe shift to reduce impact due to shift. During cruise, the lockup clutch is engaged and is disengagedduring shifts, which improves fuel economy and emissions.

OBD II for L & MD VehiclesSTD ManualOBD II Standards Manual:HS-3000 manual contains two sets of documents.Diagnostics Committee documentsMultiplex Committee documents.The following standards are in the Diagnostics Committee documents:SAE J 1930 Diagnostic Terms, Definitions, Abbreviations, and AcronymsSAE J 1962 OBD II Diagnostic ConnectorSAE J 1978 OBD II Scan ToolSAE J 1979 Diagnostics Test ModesSAE J 2012 Trouble Code DefinitionsSAE J 2186 Data Link SecuritySAE J 2190 Enhanced E/E Diagnostics Test ModesSAE J 2201 Universal Interface for OBD II ScanSAE J 2205 Expanded Diagnostic Protocol For OBD II Scan ToolsThe following standards are in the Multiplex Committee documents:SAE J 1850 Class B DATA Communications Network InterfaceSAE J 2178/1 Class B DATA Communications Network Messages:Detailed Header Formats & Physical Address AssignmentsSAE J 2178/2 Class B DATA Communications Network Messages :Data Parameter DefinitionsSAE J 2178/3 Class B DATA Communications Network Messages :Frame IDs For Single Byte Forms OF HeadersSAE J 2178/4 Class B DATA Communications Network Messages :Message Definitions For Three Byte Headers

OBD II for L & MD VehiclesSTD ManualOBD II has ten (10) major monitoring requirements: nine specific ic monitors and one catch all. Thenine monitors are: 1. Catalyst 2. Heated Catalyst 3. Misfire 4. Evaporative system5. Secondary Air System 6. Air Conditioning System Refrigerant (for CFC only) 7. Fuel system8. Oxygen Sensor 9. Exhaust Gas Recirculation (EGR) system. 10. Comprehensive components(sensors- inputs & actuators-outputs)outputs)The comprehensive components are mostly inputs and outputs to the powertrain which are sensors, andactuators. These have to be tested for circuit continuity, stuck k at 1 and stuck at 0 (ground) faults,and for range/performance problems, and internittent faults..OBD II has to communicate the diagnostic information to the vehicle mechanic via a communicationnetwork using diagnostic trouble codes (DTCs(DTCs).A special Connector , SAE J 1962, is used to facilitate the interface for communication.The mechanic uses Scan Tool, SAE J 1978, to collect diagnostic messages from the vehicle.The HS-3000 Manual specifies SAE standards for the above OBD II tools. Each SAE standardspecifies one particular component for compliance. The requirements for each SAE standard aredescribed below:

OBD II for L & MD VehiclesSTD ManualOBD II diagnostics are required to comply with SAE standards listed in the Hs-3000manual. They relate to the following areas:SAE J 1930 defines the diagnostic terms applicable to electrical/electronic systems, includingmechanical terms, definitions, abbreviations, and acronyms. These e terms only should be used by OBD II.The standard will be continuously updated by SAE for compliance by OBD II in future.All documents related to emission-related vehicle and engine service procedures shall conform to the emission relatednomenclature and abbreviations provided in SAE J 1930. This also applies to all new documents printed or updated by amanufacturer starting 1993 model year.Common names for components and systems are recognized as beneficial for technicians working on multiple models ofvehicles. Powertrain terms are approved in 1993. The standard is updated periodically y by the task force.SAE J 1962 defines minimum set of diagnostic connector requirements ents that all diagnostic toolsmust satisfy to perform OBD II monitoring and diagnostic functions on board the vehicle.SAE J 1962 is a 16 pin connector located under the instrument panel on the driver side of the vehicle.The pin assignments are specified in the standard for SAE J 1850 serial data link (2 pins), Battery power (pin 16), Battery ground,Signal Ground (pin 5), and ISO 9141 serial data link (2 pins). Connector Cterminals 2,7,10, and 15 must be compatible with theassignment and use of their mating terminal in the vehicle connector. Chassis ground is pin 4 and is defined in SAE J 2201.Battery ground must be noise free and a clean signal ground. These are intended for compliance through out the motor vehicleindustry. The SAE standards are under the control and maintenance e of the Vehicle E/E System Diagnostics Committee.

OBD II for L & MD VehiclesSTD ManualThe salient features of the SAE J 1962 standard that specifies the tOBD II’s diagnostic connector are:Consistent location in the vehicle’s instrument Panel (IP), Easeof access to technician, Ease of Visibility to the technician, and aEase of attachment of equipment without affecting normalvehicle operation.The Connector design must be compatible with previousvehicle configurations, must meet the electrical (10 A DC), andmechanical specification of material, shape, matingrequirements, and terminal assignments.

OBD II for L & MD VehiclesSTD ManualOBD II Scan Tool ( SAE J 1978 0):SAE J 1978 standard defines the requirements of the OBD II Scan Tool.This is an important function of OBD II. The Scan Tool must support the following OBD II functions:1.Automatic hands-off determination of the communication interface used.2. Obtaining and displaying the status and results of vehicle’s on-board diagnostic evaluations.3. Obtaining and displaying OBD II emissions related diagnostic trouble codes (DTCs(DTCs).4. Obtaining and displaying OBD II emissions related current data.a.5. Obtaining and displaying OBD II emissions related “freeze frame” data.6. Clearing the storage of OBD II emissions related diagnostic trouble tcodes, OBD II emissionsrelated “freeze frame” data storage and OBD II emissions related diagnostic test status.7. Ability to perform Expanded Diagnostic protocol functions as described in SAE J 2205.8. Obtaining and displaying OBD II emissions related test parameters and results as described in SAE J 1979.9. Provide a user manual and/or help facility.The Universal interface (SAE J 2201) requirements for Scan Tool ol (SAE J 1978) , Data CommunicationNetwork Interface (SAE J 1850) , (SAE J 1850) , Interface connector (SAE J 1962) requirements , Test Modes(SAE J 1979) , and Diagnostic Trouble codes (SAE J 2012), and Enhanced test modes (SAE J 2190), aredescribed in detail in the standard. General characteristics, electrical ectrical and mechanical characteristics are alsodescribed in the HS-3000 standard. EPA regulation is that SAE J 1978 must have the capability to perform bi-directional diagnostic control. Vehicle manufacturers will use manufacturer mspecific messages to performthese functions, and later use SAE J 2205, (Expanded Scan Tool protocol) pto enable these functions with SAE J 1978 Scan tool.

OBD II for L & MD VehiclesSTD ManualDiagnostic Test Modes (SAE J 11979):SAE 1979 defines the diagnostic test modes, and request and response messages necessaryto be supported by the vehicle manufacturers and test tools to meet EPA related OBD II requirements.These messages are for use by the service tool capable of performing rming OBD II diagnostics.Diagnostic test modes from mode $01 to Mode $08 are described in the standard. All test Modesexcept mode $ 08 are related to Request for Powertrain’s emission related diagnostic data or test resultsor Diagnostic trouble Codes. Test Mode $ 08 is Request for Control ol of On Board system instead of thedata. All these requests are made by the Scan Tool SAE J 1978.Mode $01 is request current powertrain diagnostic data which are:uAnalog inputs and outputsuDigital inputs and outputsuSystem status informationucalculated valuesMode $ 02 is request powertrain “Freeze Frame” data for the same items listed aboveMode $03 is request emission-relatedPowertrain Diagnostic Trouble Codes (DTCs(DTCs).Mode $04 is Clear/Reset emission related diagnostic information.Mode $05 is request Oxygen sensor monitoring test results.Mode $06 is request on-board monitoring test results for non-continuously monitored systems.Mode $07 is request on-board monitoring test results for continuously monitored systems.Mode $08 is request control of on-board system test, or component.For each test mode this standard specifies:uFunctional description of test mode.uRequest and response message formats.Examples of messages are included in the standard for explaining some complex test modes .The diagnostic message format, response time (100 ms) and various related data items are described indetail in the standard. PID $1D in table for Mode $01 is added as alternate locations for Oxygen Sensor.PID $1E in table for Mode $01 is added for Auxiliary input status. There are 14 figures showing 14 tables describingPIDs, , and messages for different Modes with their explanation including ing the method to determine if the data is valid.

OBD II for L & MD VehiclesSTD ManualDiagnostic Trouble Codes (SAE J 2012):SAE J 2012 defines the Diagnostic Trouble Codes (DTCs(DTCs) ) for OBD II. This standard focuses ondiagnostic code format and code messages for automotive electronic control systems of all light andmedium duty vehicles. The DTCs are defined by four basic categories. General Circuit Malfunction,Range/Performance Problem, Low and High Circuit input. The DTC consists of an alpha-numericdesignator, B0-B3 B3 for Body, C0-C3 C3 for Chassis, P0-P3 P3 for Powertrain, , and U0-U3 U3 for NetworkCommunication, followed by three digits. P0-P3 P3 for Powertrain is OBD II’s main concern.Diagnostic Trouble Codes are defined to indicate a suspected trouble or problem area as a directive to the proper serviceprocedure. The DTC is intended to indicate only a malfunction needing eding service and not when vehicle functions are normal.The decision to illuminate the MIL (Malfunction Indicator Light) for any DTC is based on how the system malfunctionaffects emissions.The standard has DTC code groupings designated as SAE Controlled, , Manufacturer Controlled, andreserved for future use. This prevents any manufacturer to change e any SAE Controlled DTCs and SAE tochange Manufacturer’s DTCs.Each defined fault code is assigned a message to indicate the circuit, component, or system area that wasdiagnosed as faulty. The messages are organized such that different ent messages related to a particularsensor or system are grouped together. Each group has a generic code as the first Code/Message thatindicates the generic nature of the fault. The manufacturer has a choice to define more specific DTC foreach lower level fault in that group. However only one Code must be stored in OBD II for each faultdetected. The manual gives examples of how to devise Codes to comply with the standard.Appendix C of the manual gives the Powertrain diagnostic trouble codes (DTCs(DTCs) ) as P codes.

OBD II for L & MD VehiclesDiagnostic Trouble Codes (SAE J 2012):STD ManualData Link Security (SAE J 2186):SAE J 2186 defines the security practices that must be implemented ed in accessing Diagnosticinformation only by authorized persons. The standard defines several eral levels of accessibility, likesecured functions, unsecured functions, and read only data. The emission related data isaccessible only to authorized personnel from EPA, responsible to ensure that the standard iscomplied with.Computer-coded engine operating parameters shall not be changeable without t the use ofspecialized tools and procedures accessible to only authorized persons. pAny reprogrammable computer code shall employ proven methods to deter unauthorizedreprogramming.CARB and EPA require that enhanced tampering protection for the 1999 model year that shallinclude data encryption and electronic access to manufacturer computer for security access.Procedure is defined to provide legislated “tamper protection”, while meeting manufacturerdesired security concerns for tamper resistance and allowing legitimate service.One such technique enables certain operations such as Block download only if security access issuccessful. Normal communications are not affected.

OBD II for L & MD VehiclesSTD ManualEnhanced Test Modes (SAE J 2190):SAE J 2190 extends the diagnostic test modes defined in SAE J 1979 to include access to emissionrelated data not included in SAE J 1979 and access to non-emission relate data as a supplement toSAE J 1979. This standard describes the data byte values for diagnostic messages transmitted betweendiagnostic test equipment, either on-vehicle or off-vehicle, and vehicle electronic modules. No distinction is made between emission and non-emissionrelated diagnostics. These messages can be used with J 1850 data a link as described in SAE J 1850 standard.SAE J 2190 includes test modes identified for diagnostics beyond minimum regulated requirements, that include non-emission systems. Test modesinclude capabilities such as:• Request diagnostic session• Request diagnostic “Freeze Frame” data• Request Diagnostic Trouble Codes/status• Clear diagnostic information• Request diagnostic data• Security access• Disable /enable normal message transmission• Request / define diagnostic data packets• Enter /exit diagnostic routine• Request diagnostic routine results• Input /output control• Read /write block of memoryMessages must be used with SAE J 1978 Scan Tool only using EDP protocol, pand with enhanceddiagnostics tools.This activity is also coordinating with ISO diagnostic services task force to promote commondiagnostic capabilities throughout auto industry.

OBD II for L & MD VehiclesSTD ManualEnhanced E/E Diagnostic Test Modes:The following extended diagnostic Test modes are in force:uMode Mode 10- Initiate diagnostic operation (limited)uMode Mode 11- Request module resetuMode Mode 12- Request diagnostic “Freeze Frame “ datauMode Mode 13- Request DTC informationuMode Mode 14 - Clear diagnostic informationuMode Mode 17- Request status of DTCsuModeMode 18- Request DTCs by StatusuMode Mode 20 - Return to Normal OperationuMode Mode 21-2323 - Request Diagnostic Data by PID(s)uMode Mode 2A - Request Diagnostic Data Packet(s)uMode Mode 2C - Dynamically Define Diagnostic Data PacketuMode Mode 3F - Test Device PresentuMode Mode 7F - General response MessageuMode Mode AE - Request device Control

OBD II for L & MD VehiclesSTD ManualEnhanced E/E Diagnostic Test Modes:For each test mode this standard gives a functional descriptionof the test, request message data byte content and reportmessage data byte content , and an example for clarificationwhere necessary.Physical addressing is used for all diagnostic messages in thisstandard. Each device must be assigned a unique address in thisscheme which is the method J 1850 uses to communicate withdevices.Messages 0 to FH and 40H to 4FH are reserved for SAE J 1979.Messages for J 2190 start at 10H and endat FFH. The standard defines the message length, messageresponse requirement, and their formats.

OBD II for L & MD VehiclesSTD ManualUniversal Interface for OBD II SCan Tool:SAE J 2201 defines the vehicle communication interface for OBD II Scan Tooldescribed in SAE 1978. This interface connects the SAE J 1962 test connector to thehardware/software of the SAE 1978 OBD II Scan Tool which will use uthis interface tocommunicate with vehicles for accessing required OBD II functions. The interfacedefines several standard terms and interface functionality. The standard describes indetail the software requirements of the program in the PCM that facilitatescommunication between the Scan Tool (external) and the internal OBD IIcomponents in the vehicle. The medium of communication is the serial data linkdescribed in SAE J 1850.The standard defines the required message structure support, signal ground, chassisground, cable length of the Connector to Scan Tool, and other requirements used bySAE J 1978 Scan tool.Appendix A of the standard gives examples of interface implementation that havemet the requirements of this standard.

Expanded Diagnostic Protocol for OBD II Scan Tools:SAE J 2205 defines the expanded diagnostic protocol (EDP) for OBD D II Scan Tool (SAE J 1978). The purpose of the expanded diagnostic protocol is todefine the encoding technique to be used:• To describe to the OBD II Scan Tool the messages to be transmitted to a vehicle and how they are to be transmitted.• To describe to the OBD II Scan Tool the messages to be received and processed by the Scan Tool.• To describe to the OBD II Scan Tool how to process the data in the received message.This standard defines the requirements for diagnosis and service information to be provided by motor vehicle manufacturers. Appendix A includesexamples of the use of the EDP protocol that the Scan Tool must support. This includes at a minimum, supporting diagnosing and servicing emission-relatedcomponents and systems. EDP is a means for allowing vehicle manufacturers to communicate, through the OBD II’s communication interface, withvehicle modules using vehicle specific messages.The protocol will enable the service technician to input messages s not required to meet specific OBD II requirements but which are anecessary to repairvehicles. These additional messages will be specified in service information provided to the service technician by the manufacturer. This is due to therequirement that vehicles must be able to be repaired using only a SAE J 1978 Scan Tool and other non-microprocessor based tools.The standard defines the functionality that will support the use of the Scan Tool.This standard provides the following EDP definitions:• Control type• Transmit type• Receive only type• Miscellaneous typeThese message formats are defined in the standard. The codes for EDP definition fields of the format are defined. Extensive message format informationis included which needs to be supported by the Scan Tool. This standard srequires that SAE J 1978 OBD II Scan Tool must support the tEDP messageswhich may be unique to a given vehicle manufacturer, model year, , etc. These messages may have different message headers, and different data fieldscompared to the SAE J 1979 message formats. The EDP must support ISO 9141-2 2 interface as well. The extended protocol regarding message formats, fvalidation of data , data security, and other details are explained in the standard.

OBD II for L & MD VehiclesSTD ManualCLASS B Data Communications Network Interface - SAE J 1850:CLASS B Data Communication Network Interface - SAE J 1850 standard defines the communication requirements of the tnetwork that satisfies the needs of the vehicle manufacturers to perform OBD II functions in a cost effective manner.This standard describes two specific implementations of the network based on 10.4 Kbp/ / Variable Pulse Width Type (VPW),and another at 41.6 Kbp/s Pulse Width Modification (PWM). The 10.4 Kbp/s version uses single wire and the 41.6 Kbp/s uses2-wire differential bus as the media/physical layer for message standard sdefines the physical layer and the data link layer ofthe ISO (International standards Organization) open system Interconnect (OSI) model. As a consequence this standard followsthe ISO conventions but uses different descriptive styles to define the message formats. The vehicle application for this class Bnetwork is defined in SAE J 1213 to allow sharing of the vehicle parametric information. Also the class B network must becapable of performing Class A network functions which operate at less than 10 Kbp/s.J1850 data communication network interconnects different electronic modules on the vehicle using an Open architectureapproach. Open architecture approach allows addition or removal of any number of modules in the network withoutadverse effect on the network performance. J 1850 uses CSMA (carrier rier sense multiple access) protocol to implement Openarchitecture. Additionally the network supports theprioritization of message frames such that in case of contention, n, the higher priority frames win the arbitration and completetheir transaction. The standard defines a single-bus topology where all the devices on the network transmit and receive ron asingle path at the same time with identical communication data. The network uses a Masterless bus control and priorityarbitration. The consequence of this protocol is indeterminate latency land peak bus utilization profile, except the highestpriority message is guaranteed minimum latency at the expense of other messages.

OBD II for L & MD VehiclesSTD ManualCLASS B Data Communications Network Interface - SAE J 1850:Although this standard focuses on the physical, and data link layers in the OSI model, theapplication layer is also described since this needs to be included for emission-related,diagnostic communication legislation requirements. The class B network maps into the OSImodel as illustrated in Figure 1 of the standard. The standard describes din detail the data linklayer’s diagnostic messages, their formats, physical addressing of the devices, bus protocolcommands, error detection and correction schemes. The physical dimensions dof the networkand its electrical characteristics are described in detail.Appendix A lists the application-specific features. Appendix B defines the I/O EMC test planfor the electro magnetic compatibility test to regulate electrical noise of the data signals.Appendix C gives the VPW wave form analysis that specifies the data dsignal wave formcharacteristics for the 10.4 Kbp/s version. Appendix D gives the PWM wave form analysis thatspecifies the data signal wave form characteristics for the 41.6 Kbp/s version.SAE J 1850 is the most important standard in the Data Communication ion phase of the OBD II.

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Detailed Header Formats and PhysicalAddress Segments: (SAE J 2178/1):SAE J 2178/1, is the Class B Data Communication Network Messages’ s’ Detailed Header formatsand Physical Address Assignments specification. The standard defines the informationcontained in the header and data fields of non-diagnostic messages. The standard also specifiesfield sizes, scaling, representations, and data positions used within messages. The generalstructure of the message frame is described with inframe response included in Figure 1 andwithout the response in Figure 2 of the standard. SAE J 1979 standard defines the informationcontained in the header and data fields of emission related diagnostic messages. SAE J 2190standard defines the information contained in the header and data a fields of other diagnosticmessages not related to emissions. SAE J 1850 standard defines the class B network interfacehardware, basic protocol definition, the electrical specifications, and the error detection-correction scheme using CRC (cyclic redundancy check) Byte. SAE J 1850 defines only twomessage formats. They are the single Byte format and the consolidated header format. Theconsolidated header format has two forms: a single Byte form, and d a three byte form. Thisstandard covers all these formats and forms to identify the contents of messages which can besent on the SAE J 1850 network.

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Detailed Header Formats and PhysicalAddress Segments: (SAE J 2178/1) (contd(contd):SAE J 2178 consists of four parts. SAE J 2178/1, the first part (this standard) describes the two allowed formsof message header formats, Single Byte, and Consolidated header formats. This also contains the physicalnode address range assignments for the typical subsystems of the e automobile.The standard defines the terms and definitions of the data formats. The overview of the standard is given inFigure 3 of the standard. The system architecture for the different ent possible headers used in class B aredescribed in sections 5 and 6. Section 7 defines the data fields used by the different headerformats. section 8 defines the physical address assignments. Messages sages defined by this standard are classifiedinto two categories: Requests (commands: load or modify) or queries for data, and Responses, like reports oracknowledgments. The overall structure of messages is described as follows:• Fully define SAE standard messages• Reserve messages for future SAE standardization• Reserve messages for Manufacturers for their Unique messagesThe message formats in this standard are mandatory for using J 18501network except the many messagecodes reserved for manufacturers which are allocated can be used.Appendix A describes two allowed network architectures, namely single snetwork, and multiple networkarchitectures.

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Data Parameter Defintions: : (SAE J2178/2):SAE J 2178/2 Data Parameter Definitions standard defines the parameters ameters used todescribe the data variables used in normal vehicle operation as well as diagnosticoperation. Parameters are assigned Parameter Reference Numbers (PRNs(PRNs) ) which aredescribed in the standard. PRN structure is shown in Figure 3 in the standard. Thesecond part of the parameter definition is the SLOT. PRN identifies ies a specificparameter by name, unit measure , and its associated SLOT. The SLOT Sdefines themathematical characteristic of parameters in terms of its numeric presentation, itsscaling, its limits, Offsets, and its transfer function.Appendix A and B provide cross references to find the PRN by the number or byname. PRN structure is given in Figure 3. SAE J 1979 refers to PID Pnumbers whichare single byte reference number. The first 256 PRNs defined in this standard areidentical to the SAE J 1979 PID definitions. The standard contains ns detailed lists ofPRN assignments which are used for reference.

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Frame IDs For Single Byte Formsof Headers (SAE J 2178/3):SAE J 2178/3 Frame IDs for Single Byte Forms of Headers standard, d, defines the messages specified fornetworks using one byte header or the single byte form of the consolidated header as specified in SAE J 1850.This standard focuses on the Frame ID which is the first byte of the message. The first byte of the one byteheader is defined as an 8 bit hexadecimal number, and the first byte of the single byte form of theconsolidated header is defined under 7 bits as hexadecimal number. The information in the header fieldimplicitly defines the target, source, priority, and message type e information, while the data field containsadditional addressing and parametric information. The header defines the Message identifier or Frame IDand becomes the name that is broadcast normally periodically to all the nodes on the network.This standard describes the overall structure of messages and has s wide application in OBD II since these haveto be used on J 1850 exactly as they are specified here, except those that are allocated to vehicle manufacturersfor non-emission related messages.With single byte form of header, the Frame ID corresponds to the PRN number or a grouping of PRNs. . Thecharacteristics defined by the header are described in the standard. ard. Figure 3 of the standard defines theFrame ID for one byte headers and the first byte of the single byte bform of the consolidated header.

OBD II for L & MD VehiclesSTD ManualClass B Data Communication Network Messages- Message Definition for Three ByteHeaders (SAE J 2178/4):SAE J 2178/4 Message Definition for Three Byte Headers, standard defines the informationcontained in the header and the data fields of non-diagnostic messages for SAE J 1850 datacommunication class B networks. This standard describes and specifies the header fields, datafields, field sizes, scaling, representations, and data positions s used within messages. SAE J 1979standard defines the specifications of emission-related diagnostic message header and datafields which OBD II is mainly concurred with. SAE J 2190 defines other diagnostic data fields.This standard focuses on the message definition for the three byte form of the consulted headerformat. Section 5 of this standard provides the list of functional target addresses or Primary IDsfor all of the functionally addressed messages on J 1850 except type #3, which is Function Read.SAE J 1850 type # 3 messages have a separate address assignment due to absence of secondaryaddressing. Section 6 of the standard shows the valid extended address aassignments from themessage definition tables. Section 7 lists the secondary message definitions. The information inthis standard follows the same format as the Frame IDs for Single e Byte Forms of Headersin SAE J 2178/3 standard described above.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsSince OBD II became effective in 1994 ( adopted from CARB regulations),powertrain control strategies are focused on monitoring powertraincomponents for failures with criteria tied to emission levels in addition tobasic functionality. All the powertrain components described in previoussection on Powertrain and Emission Controls in Passenger vehiclesincluding sensors, actuators, and switches are checked for correct operation.In addition the performance of emission control apparatus are continuouslymonitored using OBD II Diagnostics criteria. The following is a list of themajor CARB related OBD I I diagnostic requirements for all vehiclemanufacturers:

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsOBD I I Diagnostic RequirementsuEngine Misfire DetectionuCatalyst Efficiency MonitoruOxygen Sensor & Heater MonitoringuFuel System MonitoringuEvaporative System MonitoringuEGR System MonitoringuSecondary Air System MonitoringuComprehensive Components Monitoring (all sensors,actuators, and switches)

Engine Misfire Detection: Misfiring is the lack of combustion in the cylinder. Misfiring can be caused by worn ignitioncomponents, poor fuel metering, or faulty electrical system. Excessive exhaust emissions will be the result even with fewmisfires. Increased misfire rates can damage the catalytic converter. Engine misfire is detected by monitoring crankshaft speedfluctuations. Engine misfire willcontribute to a deceleration of the crankshaft’s rotational speed d due to the momentary absence of engine torque during thepowerstroke of the cylinder that is misfiring. Using the crankshaft sensor input, theinstantaneous crankshaft speed is calculated, and the speed signal is analyzed to detect the misfire. To eliminate other causes oftorque reduction due to rough roads and other driving events, the e speed reduction is monitored using Exponentially weightedmoving average (EWMA) technique to identify the misfiring cylinder. Other techniques used to identify torque reduction due tomisfire, include signal processing using several algorithms. One signal processing method analyzes the amplitude and phase ofeach of the first twelve frequency components of the crankshaft angular velocity signal taken continuously during the torquereduction time. If a certain percent of misfires within 200 or 10001revolutions is detected , a fault code (DTC) is set. Misfire isdetected if the offending cylinder can be identified. Other advanced anced signal processing algorithms can be used such as PrincipalComponent Analysis and Clustering to compress the data and isolate the misfiring cylinder.If a misfire is detected, all the main engine operating parameters rs such as engine speed , engine load or MAP (Manifold absolutePressure), engine coolant temperature, throttle position, oxygen n sensor, values are stored away in memory. This is called“Freeze Frame”, which is an OBD II requirement. Freeze Frame is used to identify a consecutive misfire in the next driving cycledefined by the EPA as the next driving “Trip” after ignition OFF. . If a second misfire is detected the engine controller will turnon the MIL (Malfunction Indicator Light) to alert the driver. The e specific cylinder experiencing misfire must be identified. Ifmore than one cylinder is misfiring a separate DTI (diagnostic trouble tcode) is required.If misfire is not detected during the next three subsequent consecutive driving “Trips” when similar conditions occur then theoriginal fault will be erased and the MIL will be turned off by the engine controller. In another circumstance , if “similarconditions” are not encountered during next eighty subsequent trips the original fault will be turned off by the enginecontroller.

The Freeze Frame can also be used for Off-Board diagnostics and trouble shooting by service technicians.Misfires can damage the catalyst converters by raising the catalyst temperature beyond safe values.Type A misfire is defined below:For type A misfire, up to three 200 revolutions are evaluated on first driving cycle for misfire detectionbefore illuminating MIL.MIL must be illuminated on misfire detection during first 200 revolutions’ evaluation during the second driving cycle.However MIL need not be steadily illuminated when misfire ceases, , until second driving cycle.Type B misfire (during starting of engine):This misfire is evaluated in first 1000 revolutions after engine is started. Misfire detection will set coolant temperaturefault code since that is the likely cause of misfire detection at this time.MIL and “hard” fault code is set permanently on second driving cycle. cUp to four 1000 revolutions are evaluated for misfire detection excluding the first 1000 revolutionsbefore illuminating temperature fault code.MIL and “hard code” are set on second driving cycle.Thermostat (coolant temperature) monitoring and misfire detection n monitoring are extremely important due toincreasingly tighter controls mandated on emissions.Misfire detection is described in more detail in a later section.

Catalyst Efficiency Monitor: There are three types of catalysts: pellet (bead), ceramic monolith, and metal monolith. They differin the method by which they support the noble metals which convert exhaust gases to HC and NOx free gases. Three-waycatalytic converters typically contain platinum, and/or palladium, along with rhodium as catalytic materials. The term three-way refers to the ability of the converter to simultaneously oxidize HC and CO and reduce NOx. . Catalyst converters operateefficiently within a prescribed temperature range when placed at proper location in the exhaust gases’ path. Operation attemperatures which exceed the recommended maximums may cause irreversible damage to the catalyst, and components of theconverter. Since unburned fuel into the converter can cause catastrophic astrophic failure, misfire detection is a must for safe converteroperation. Misfire detection is described previously. Converter also must have an over temperature detection algorithm todetect excessive temperature in the converter. This is done by decreasing dthe A/F ratio’s lambda value to less than 1. Thisalgorithm cannot work for coastdown conditions or overrun conditions. Therefore Deceleration fuel cutoff c(DFCO) is sued tocontrol catalyst temperature during vehicle coastdown, , when the engine intake manifold pressure is drive too low to allow acomplete combustion. To prevent unburned fuel from entering the converter, the fuel injectors are shut off by the enginecontroller. Spark advance is filtered and thresholds are set to control torque reversal ”bump” while still protecting the converter.The catalyst monitor evaluates the converter efficiency as mandated by the OBD II to ensure that the catalyst is cleaning up theexhaust gases and reducing emissions from the exhaust gases. The diagnostic evaluates the oxygen storage capacity of theconverter by comparing the signal output of the post-converter oxygen sensor with the pre-converter oxygen sensor. Accordingto EPA regulations, a catalyst is regarded as malfunctioning when n the average hydrocarbon conversion efficiency falls between50 and 60%. The diagnostic system is required to detect when the hydrocarbon emission (HC) concentration of the catalyst(closest to the engine ) is more than 40 to 50% of the engine-out emission concentration. The check is performed with the vehicleoperating at between 20 and 50 miles/hr with the speed held at a reasonably steady state condition. The output signal waveform of the oxygen sensor (lambda sensor) ,at the front end of the tconverter close to the engine, oscillates between lean and richvalue of 100 millivolts and 900 millivolts due to closed-loop loop control strategy that keeps the Air/Fuel ratio at stoichiometry(lambda value equal to 1). For a converter whose oxygen storage e capacity is good, the output of the oxygen signal at the far end eof the converter should be flat, without any oscillation. This is due to the converter’s ability to store oxygen when the gas is lean(and rich in oxygen) and give up oxygen when the gas is rich (and d short of oxygen). This characteristic enables the oxidation ofhydrocarbons and the reduction of NOx in the exhaust gas simultaneously. The diagnostic consists of measuring mthe averageripple in the output signal wave form of the oxygen sensor at the e far end of the converter and comparing the ripple with asimilar oscillation at the input signal wave form of the oxygen sensor at the near end (closest to the engine) of the converter. Ifthe difference is above a value that corresponds to more than 60% 6converter efficiency then the converter efficiency isconsidered good. As a second check the catalyst temperature at the toutlet is monitored and compared to the catalysttemperature at the input to the converter. If the catalyst is functioning properly, it creates an exothermic reaction resulting in ahigher outlet catalyst temperature. But this is not always reliable. The sensitivity of the outlet gas temperature to catalystefficiency may be too low to reliably detect the difference at the t60% HC conversion efficiency level.Signal characteristics from the oxygen sensors for fresh, degraded, ed, and failed catalysts are explained in detail in a later section.The misfire detection diagnostic which is previously described is an important preventive measure that protects the converterfrom extreme temperature spike that can severely reduce converter r efficiency or even cause catalyst destruction altogether.Catalyst converter diagnostics are described in more detail in a later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsOxygen Sensor & Heater Monitoring: An oxygen sensor performs best t when its operating temperature is maintained within a specific range above 260 O C. For this reason aheater is used to keep the oxygen sensor temperature at the desired value.The OBD II diagnostic requires that the heater of the oxygen sensor sor must be monitored periodically for its normal operation. The circuit continuity is checked, the voltageacross the heater is checked, the current carried by the heater element is checked ( Max. 20 A), as well as the temperature of the toxygen sensor. For added reliability, theheater is directly controlled by the the controller without any relay. If the heater is found defective on any of these accounts, the PCM sets a fault code.The PCM has a special input circuit for detecting short circuit or open circuit (break) of the sensor wiring and monitors the switching frequency (closed-loop) loop) of the controlloop.Oxygen sensor diagnostic requires the following checks: Circuit continuity ,and the bias voltage of 450 millivolts in the sensor circuit are verified. The voltage across thesensor should read 450 millivolts with the ignition key On and engine not started. If the voltage is not present a fault code (DTC) isset. During the closed loop operation of the vehicle, after the sensor attains the operating temperature (above 300 O C ), the sensor voltage should oscillate between about100 to 250 mv at the low end and 700 to 900 mv at the high end. The frequency of oscillation of this sensor voltage is between 1.25 Hz to 2.5 Hz, depending upon the fuelcontroller, fuel injection system, and vehicle operation. If the oscillation is slower than normal meaning that the oxygen sensor r is responding slowly to the A/F ratio input,then it is due to the sensor being exposed to high heat for a long period of time. This can cause a deviation in the A/F ratio from fthe optimum stoichiometry value,resulting in increased emissions. The deviation can be detected by monitoring the signal output oscillation of upstream oxygen (lambda) sensor and comparing it with thesystem operation frequency (1.25 Hz to 2.5 Hz) obtained from the e controller. A fault code is stored if the oxygen sensor at the upstream of the converter is oscillatingslower than the system frequency. A MIL is also illuminated. Additionally the controller compares the output signal (voltage) of the additional lambda sensor downstreamof the converter with the oxygen (lambda) sensor signal upstream. . Using this information the controller can detect deviations of the average value in the A/F ratio thatdetermines the system frequency. If system is operating rich and the lambda sensor indicates lean, then it is misfire problem. If system is operating lean, and the lambdasensor voltage stays near bias (450 mv) ) and engine does not go into closed loop, the sensor is having an open circuit and is defective. Slow transient response in A/F shiftcan also be caused by fuel control problem or carbon deposits or due to mild driving mode. Fuel system must be checked before deciding that oxygen sensor is faulty. If theA/F ratio is fluctuating due to excessive correction, to the pre set data map of optimum fuel required for each load and engine RPM, provided by the oxygen sensor, it is anindication of a faulty fuel system. The OBD II legal requirements s are: The diagnostic system shall monitor the output voltage, the tresponse rate, and any other parameterthat can affect emissions, and all fuel control oxygen sensors for fmalfunction.all fuel control oxygen sensors for malfunction. In case of a faulty sensor the MIL shall be illuminated and the DTC shall be stored in the computer.Oxygen sensor diagnostics are described in more detail in a later r section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsFuel System Monitoring: : For fuel control strategies multipoint pulsed fuel injection system sis assumed. The powertrain control strategy is to provide thecorrect Air/Fuel ratio under all operating conditions, except during cold-start. The systems involved in this control are fuel metering, fuel fpump, ignitiontiming, fuel injectors, injector pulse width, and lambda control. . The PCM determines the required injector pulse width to maintain Air/Fuel ratio withinthe lambda control window (0.93 to 1.07). The PCM adds correction n factors to injectior pulse width to increase fuel injection during cold start, and wide wopen throttle, in closed-loop loop operation. During deceleration, PCM closes fuel injection. Ignition timing affects emissions. Excessive spark advance willcause engine knock. consequently fuel system monitoring is done by using predetermined data map with optimal fuel required for each load (MAPvalue) and engine RPM point. The amount of fuel is determined by the duty cycle of the injector pulse width.The lambda closed-loop loop control system provides feedback to the PCM on the necessary y correction to the preset data points. The corrected informationis stored in the PCM’s memory so that the next time that operation point is reached, less lcorrection of the Air/Fuel ratio will be required. If the PCMcorrection passes a predetermined threshold, it indicates a faulty fuel system, that some component in the fuel supply system is outside of its operatingrange. Some possibilities are defective fuel pressure regulator, contaminated fuel injectors, defective manifold absolute pressure (MAP) sensor, intake airsystem leakage, or exhaust system leakage. All electronic components are checked for circuit continuity, rated current, rated voltage, vand rationalparameter values within limits of operation. These include fuel pump, ignition circuit, injection solenoids, engine RPM sensor, and MAP sensor. If thefuel correction exceeds the limit, either in absolute value or in update rate, the fuel system is deemed faulty and a fault code is stored and MIL isilluminated. Since fuel system has a major impact on emissions, its diagnostics are crucial to control emissions and consequently y to OBD II.The legal OBD II requirements are: The diagnostic system shall monitor mthe fuel delivery system for its ability to provide compliance with emissionstandards.Diagnostic technique: Deviations of the stoichiometric ratio which last for a longer time are stored within the adaptive mixture controller. If thesevalues exceed defined limits, components of the fuel system are deemed faulty. MIL is illuminated at that time. Fuel system diagnostics are described inmore detail in a later section.

Evaporative System Monitoring: Hydro Carbons (HC) in the form of fuel vapors escaping from the e vehicle, primarily from thefuel tank are required to be monitored to reduce emissions as legislated by EPA and required by OBD II. There are two principalcauses of fuel vapor in the fuel tank: increasing ambient temperature and return of unused hot fuel from the engine. Theevaporative control system consists of a vapor ventilation line that exits the fuel tank and enters fuel vapor canister. The canisterconsists of an active charcoal element which absorbs the vapor and aallows only air to escape to the atmosphere. Only a certainvolume of fuel vapor can be contained by the canister. The vapors s in the canister must therefore be purged into the engine andburned by the engine so that the canister can continue to store vapors when they are generated.To accomplish this another purge line leads from the char coal canister cto the intake manifold. Included in this line is thecanister purge solenoid valve. The layout of a typical evaporative ve emission control system is described in a later section.During engine operation vacuum in the intake manifold causes flow w through the charcoal canister because the canister ventopening at the charcoal filter end is at atmospheric pressure. The Tcanister purge valve meters the amount of flow from thecanister. The amount of fuel vapor in the canister and therefore, , contained in the flow stream, is not known. Therefore it iscritical that the lambda control system is operating and adjusting the fuel requirement as the vapors are being purged. Purgevapors could otherwise result in upto 30% increase in Air/Fuel mixture richness in the engine. Purge control valve is situated inthe pipe line that connects the intake manifold of the engine to the charcoal canister.Control of the purge valve must allow for two criteria:• There must be enough vapor flow so that charcoal canister does not nbecome saturated and leak fuel vapors into theatmosphere.• Purge flow must generally occur under lambda closed-loop loop control so that the effect of the purge vapors on A/F ratio canbe detected and the fuel metering corrected.When the PCM commands the purge valve to meter vapor from the canister, it requests a duty cycle (ratio of ON time to OFFtime). This allows the amount of vapor flow to be regulated depending on the engine operating conditions. When lambdacontrol is not operating, during cold-start, only low duty-cycles and therefore, small amount of purge vapors, are allowed intothe intake manifold. Under deceleration fuel cut off, the purge valve is closed entirely to minimize the possibility of unburnedHCs in the exhaust.The OBD II diagnostic system shall control the air flow of the complete cevaporative system. In addition , the diagnostic systemshall also monitor the complete evaporative system for the emission ion of HC vapor into the atmosphere by performing a pressureor vacuum check of the complete evaporative system. From time to time, manufacturers may occasionally turn off theevaporative purge system in order to carry out a check.The following is the procedure: At idle position, the canister purge pvalve is activated, and the lambda controller is monitored forits reaction.A pressure sensor in the fuel tank would provide a pressure profile pwhich will determine if a leak existed in the system.For leak detection of the evaporative system, a valve installed led at the atmospheric side of the canister which is the output to theactive carbon filter is shut off and the canister pressure is decreased to about -1.5KPa. . The complete system is turned off and thepressure within the canister is monitored for variation with time. The pressure gradient, together with other parameters like theamount of fuel, will indicate possible leaks. If a leak is detected ted the MIL is illuminated. The complete test suite is moreelaborate and is described in detail in a later section.

EGR System Monitoring: During overrun and heavy load of the vehicle the peak combustion n temperature ofthe cylinders of the engine will increase to more than 3000 o F. A measured quantity of exhaust gas isintroduced into intake manifold via a pintle valve connecting the exhaust gas to the intake manifold. Bymixing a portion of the exhaust gas with fresh intake air/fuel mixture mthe oxygen content is reduced withoutreducing the mass of gas processed by the cylinder. The engine acts apartially like an external combustionengine in that the combustion process must impart energy to the inert exhaust gas as well as to the air charge.The net effect is to reduce the flame temperature at part load while wretaining the power of the engine. Thereduction of temperature reduces NOx emission produced by the engine.The OBD II diagnostic has to monitor the pintle valve, and the amount of exhaust gas delivered by the pintlevalve. The correct amount of exhaust gas is obtained from predefined engine RPM/load (MAP) table showingoptimum EGR valve openings & gas amount, engine coolant temperature, manifold absolute pressure (MAP)pressure, and engine RPM. During EGR operation, the fuel is cut off. The OBD II diagnostic consists of severalalgorithms to monitor all the functions listed above. EGR pintle valve position is monitored by the PCM forproper opening. The amount of exhaust gas ingested is monitored from the EGR pintle valve flow rate, andthe time of the valve opening. This amount is compared with the required amount obtained from the tablewith predefined values. If there is a significant difference between the actual and the needed values, the EGRmalfunction is detected. Engine coolant temperature is monitored for an increase in value during EGRoperation. MAP pressure is monitored for increase in pressure during dEGR operation. Finally the EngineRPM (900 - 1100) is monitored for a decrease of about 50 RPM during EGR (DTC for fault is P0401 for nodecrease in RPM when vehicle speed is 25 MPH with brakes applied) ) operation.

OBD(II)In addition the electrical characteristics of the pintle valve are checked, including the voltage, the current drawn bythe moving pintle, , and the circuit continuity including open circuit as well as short scircuit in the wiring. There aretwo methods used in verifying that EGR is functioning properly meaning mno sticking valve or clogged EGR passage.The first method is to intentionally open the EGR valve through a measured value during normal operation whenthere is no need for EGR and measure the response of critical system sparameters due to this perturbation namely,Engine RPM, coolant temperature, MAP pressure, pintle valve position, and closed-loop loop fuel system correction. Ifthe critical parameters do not conform to the desired values EGR malfunction is indicated. The second method is towait for the condition of the vehicle when the EGR is operated by the PCM as a consequence of engine overrun orhigh load. Then intentionally disable EGR operation for a small predefined amount of time and measure the criticalparameters. If the difference in critical parameter values do not t conform to the expected values then EGRmalfunction is indicated.A much simpler algorithm measures the increase in coolant temperature during EGR and if the increase in notwithin desired range EGR malfunction is indicated. In addition increase iin manifold absolute pressure (MAP)during EGR and if the increase is not within desired range EGR malfunction mis indicated.Due to uncertainties encountered in EGR monitoring, more than one e diagnostic is necessary before a fault code isstored and the MIL is illuminated. One method is to requires three successive tests, each revealing an EGR fault,before a fault code is stored. If a test reveals no fault , the next test is performed eleven minutes later. The predefinedoperating condition is deceleration which means that the test is performed during deceleration of the vehicle.Different frequencies of testing are also used in the diagnostic. . Another method requires eight tests to be performedwithin a two minute period before a fault code is stored when two o failures occur within that period. Currently aboutfifty percent of the manufacturers monitor the EGR passage temperature, twenty-five percent monitor the EGR valvesignal (position), and twenty-five percent use the intrusive perturbation method to detect EGR malfunction.The legal OBD II requirement is: The diagnostic system shall monitor the EGR system on vehicle for low and highflow rate malfunction.The hardware failure code of P1406 is set for out of range voltage signal from the pintle valve position sensor ofmore than 10% from commanded value.Another manufacturer monitors the exhaust gas pressures on both sides of an orifice in the passage to the EGRvalve. The pressure drop across the orifice is measured as the exhaust egas flows through the orifice. If the pressuredifferential is not within permissible limits, EGR fault code is set.Different DTCs are set for tests performed with similar EGR diagnostic objectives due to differences in test time, andcritical parameter values.EGR diagnostics diagnostics are described in more detail in a later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsSecondary Air System Monitoring: Secondary air system is used to improve the performance of the catalytic converter (Three way) by providing extraoxygen rich air to either the converter itself or to the exhaust manifold. The catalyst temperature must be above about 200 o C to efficiently oxidize HC andreduce NOx. . During engine warm-up when the catalytic converter is cold, HC and CO are oxidized in the exhaust manifold by routing secondary air tothe exhaust manifold in controlled quantify by the PCM. This creates extra heat to speed warm-up of the converter and EGO sensor, enabling the PCM togo into closed-loop loop mode more quickly.During open-loop control (cold converter) the converter is liable to be damaged if excessive heat is applied to it, to warm it up. This can happen ifexcessive amounts of HC and CO are oxidized in the exhaust manifold during periods of heavy loads which call for fuel enrichment, , or during severedeceleration. During start-up and such heavy loads, the secondary air is not let into exhaust manifold but directed into the air cleaner where it has noeffect on exhaust temperatures.After warm-up, during closed-loop loop operation, the secondary air is used to supply oxygen to the e second chamber of the three-way catalyst, in dual-chamber converter system. In a dual-chamber converter, the first chamber contains rhodium, palladium, , and platinum to reduce NOx and to oxidize HCand CO. The second chamber contains only platinum and palladium. The extra oxygen from the secondary air improves the converter’s s ability to oxidizeHC and CO in the second converter chamber. The control of the secondary air is done by using two solenoid valves similar to the EGR pintle valve. Onevalve switches air flow to the exhaust manifold or to the air cleaner (atmosphere). The other valve switches air flow to the exhaust manifold or to thecatalytic converter. The air routing is controlled based on engine ne coolant temperature and Air/Fuel ratio, indicated by the lambda sensor. If the control isopen-loop and if the coolant temperature is below threshold and Air/Fuel ratio is not too rich, then the air flow is directed to the exhaust manifold. Ifcoolant temperature is higher than threshold and the Air/Fuel ratio is rich (lambda < 1) then the secondary air is directed to the air cleaner which exitsto the atmosphere. If the control is closed-loop, loop, then the lambda sensor is monitored for correlated deviations when the secondary air flow is changedfrom exhaust manifold, or catalytic converter, or air cleaner, depending don coolant temperature, and lambda value. The OBD II requirement is that thesecondary air system shall have the diagnostic system monitor the e proper functioning of the secondary air delivery, and any air switching valve(solenoid).The critical parameters of the secondary air system are monitored d and if found to be out of permissible range of values, the fault code is set. The MIL isilluminated.Secondary air diagnostics are described in more detail in a later r section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsComprehensive Components Monitoring includes all the sensors, solenoids, fuel injectors, fuel pump, ignition coil, actuators(valves), and the associated wiring, ground, and power supply. The Tfollowing components with their DTCs are describedbelow:uManifold absolute pressure (MAP) sensor DTCs 105 - 109u Intake air temperature sensor DTCs 110-114114uOxygen sensor sensor DTCs 130 -167uMass air flow (MAF) sensor DTCs 100-104104uThrottle position sensor DTCs 120-124, 124, 220-229229uCrankshaft angle sensor DTCs 335-344, 344, 385-389389u Engine coolant temperature sensor DTCs 115-119, 119, 125-126126uKnock sensor DTCs 325-334334uEngine speed sensor DTCs 320-323323uVehicle speed sensor DTCs 500-503503uMisfire (sensor) detector DTCs 300-312312uCanister vent valve DTCs 440-455455u Purge valve DTCs 465-469469uIgnition coil (ignition control) DTCs 350-379379uFuel system (fuel metering) DTCs 170-195, 195, 230-233233uIndividual fuel injectors DTCs 251-296296uEGR sensor/ valve DTCs 400-408408uIdle air control (IAC) valve DTCs 505-507507uSecondary air valve DTCs 410-419419uFuel level sensor DTCs 460-464464uCatalytic converter DTCs 420-434434

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsThe OBD II diagnostics consist of conductingtests on all the sensors and actuators listedabove. The nature of these tests isdescribed below. If any fault is detected inany of the tests of these devices including ,sensor or actuator component, electricalcircuit, wiring, and power source, thecorresponding diagnostic trouble code(DTC) assigned in SAE J 2120 to that fault,is displayed and the malfunctionindication light (MIL)is illuminated.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsSAE J 2012 standard defines the recommended practice for diagnostic trouble codes (DTC) ofall comprehensive components listed above. The DTC consists of an alpha-numericdesignator p0 - p3 for powertrain, , where p0 codes belong to SAE controlled codes, P1 belong tomanufacturer, and the rest are reserved for future use. The P0 codes care followed by three digitcodes assigned to individual faults. The assignment of the proper r designator should bedetermined by the PCM. In case of ambiguity, the upper most nibble of the two -byte codemessage as defined in SAE J 1979 will define the source system as follows: P0 - 0000, and P1 -0001. This standard defines diagnostic trouble codes for all the circuits, components, andsystems which are controlled by SAE, namely P0 codes. The P0 codes are defined by fourdifferent categories: General Circuit Malfunction, Range/Performance ance Problem, Low CircuitInput, and High Circuit Input. Manufacturers can define specific DTCs to meet their controlleralgorithms, but all DTC words must meet the terms’ definitions specified sin SAE J 1930standard for Diagnostic terms, definitions, abbreviations, and acronyms. aThe definition of thesefour categories of faults will be described first. Then the DTCs for different faults for eachsensor and actuator listed above will be described. SAE J 2012 provides guidance (definitions)for message formats, Parameter Identification numbers (PIDs(PIDs) ) and their definitions with actualexamples for compliance. The main aspects of these definitions are acovered below. For moredetailed knowledge of the DTCs and their messages, please refer to SAE J 2012, SAE J 1979, andSAE J 1930.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsGeneral Circuit Malfunction: This is a general purpose failure resulting in the componentnot responding with expected value or any value. This could be due to short circuit in thecircuit wiring, or an open circuit, or a complete break down of the function resulting ina wrong response including no response.Range/Performance: This is the case when the component is functional in general termsexcept that the response value is not within the normal operating range. This can be due tostuck at 0 or stuck at 1 fault, or erratic, intermittent, or skewed values indicating poorperformance of the circuit, component, or system.Low Circuit Input: The circuit voltage, frequency or other signal measured at the controlmodule input terminal or Pin is at or near zero. This is measured with the external circuit,component, or system connected. The signal type (voltage, frequency) shall be included inthe message in place of the word “input”.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsHigh Circuit Input: The circuit voltage, frequency or other signal measured at the controlmodule input terminal or Pin is at or near full scale. This is measured with the external circuit,component, or system connected. The signal type (voltage, frequency) shall be included inthe message in place of the word”input”.DTC codes are grouped in different categories. Each category has 100 codes assigned to itas follows: P01 - Fuel and Air metering 100-199, P02 - Fuel and Air metering,P03 - Ignition system or Misfire 300-389, P04 - auxiliary emission controls 400 - 485,and P05 - vehicle speed, idle control, and auxiliary inputs 500 - 574, P06 - Computer andauxiliary outputs 600- 605, and P07 Transmission 700 - 790.Since OBD II focuses on emissions control only DTCs upto P04 followed by three digitfault code are covered here.DTCs are defined to indicate a suspected trouble or problem area and are intendedas a directive to the proper service procedure. DTC s should not be used to indicate theabsence of problems but only to indicate specific fault. The decision to illuminate MIL forany DTC is manufacture specific based on their testing of how each system malfunctionaffects emissions.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsCore DTCS: Core DTCs are those codes which have achieved compliance uniformlythroughout the industry. For these, a common DTC number, and fault message is assigned.Undefined DTCs are reserved for future use. Even though the service procedures forrectifying each of these DTCs may vary among manufacturers, the fault indicated bythe DTC is common enough to be assigned a particular fault code.Non-Uniform DTC: These are fault codes that have very little commonality amongmanufacturers due to system differences, implementation differences, or diagnosticstrategy differences. Manufacturers who define their own DTCs in this area areurged to remain consistent across their product line when assigning codes in manufacturercontrolled area. Same groupings should be used as in SAE controlled area, i.e.., 100s and 200sfor fuel and air metering, 300 for ignition system or misfire, etc.Each defined DTC is assigned a message to indicate the circuit, component, or system areathat is faulty. The messages are organized such that different messages related to aparticular sensor or system are grouped together. In cases where there are various faultmessages for different types of faults, the group also has a “Generic” message as the faultCode/Message of the group. Manufacturer has a choice to use the specific or generic faultcode, provided only one code is used consistently to describe that fault.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsIn a case where messages are broken down into more specific fault descriptions for acircuit, component, or system, as is done in complex cases, the manufacturer shouldchoose the fault code most applicable to their diagnosable fault. The messages areintended to allow the manufacturers to use them as often as possible yet still notconflict with their specific repair procedures. Each code should lead to a specificrepair procedure(s).Examples: As a guide to clarify the above points a few examples are given.For manufacturers choosing to implement basic diagnostics that provide generalfault information but depend on service procedures and Off-board diagnostics toisolate the problem, general circuit, component, and system codes will be used.For example, if a fault is detected in in the throttle position sensor circuit, insteadof burdening the OBD II with determining the specific type of fault, a Code P0120would be stored indicating some type of problem with that circuit. The serviceprocedure would then allow the service technician to determine the type of faultand the specific location of the fault. On these types of systems, such as sensors,actuators, coils, and switches, a shorted sensor input, an open sensor input, and evenout of range sensor output would all set the same fault code.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsHowever, manufacturers choosing to allow the OBD II to better isolate the fault to specificcause would not use the general fault code/message, but would use the more specificcode/message associated with the particular circuit, component, or system.For example, in diagnosing a 5 volt reference throttle position sensor, if the input signal atthe PCM is stuck at near 0 volt, the manufacturer has the choice to select either of two codes:P0120 (general malfunction), or P0122 (specific low circuit input ), depending on themanufacturer’s diagnostic procedures. The root cause of this fault can be any one of electricalor mechanical problems. Identification of the root cause is done using the diagnosticprocedures and is not implied by the DTC message, thus allowing the manufacturer theflexibility in assigning DTCs.The powertrain control strategies in performing OBD II diagnostics depend on eachmanufacturer who has considerable flexibility as to how the diagnostics are implementedprovided the above guidelines of SAE J 2012, SAE 1979, and SAE J 1930 are complied with.A typical use of OBD II procedure is given below as a generic example:The diagnostic mode is entered by switching on the ignition and then simultaneouslydepressing the OFF and Warmer buttons on the climate control system (cadillac).

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsThe fault codes are displayed by flashing the “Check Engine” light and entering thedisplay mode. Each fault code is displayed in sequence starting with the code thatchecks that all display segments are working correctly.After verifying that all display segments are working, the fault codes for all componentfailures are displayed in sequence, beginning with the lowest and proceeding to thehighest code. The mechanic notes the fault codes that are displayed , and using areference manual, identifies the failed components. The fault codes must comply withthe SAE J 2012 standard. After all fault codes are displayed, special code appearson the display indicating the end of display, and the engine control system awaitsfurther action by the mechanic.Typically the “check engine” light on the instrument panel is illuminated whenever anyfault occurs. For emissions related faults the MIL light will not go out until cleared frommemory by the mechanic. For non-emissions related faults the MIL light goes outautomatically if the malfunction clears. However the PCM stores the DTC associatedwith the detected failure until the diagnostic system is manually cleared oruntil a specified number of engine cycles (twenty) occur with no malfunction. Forsome DTCs (of lesser consequence) there is no activation of the “check engine” MIL light.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticswhenever a defect occurs the mechanic must follow a specific procedure to isolate theparticular problem. These procedures are outlined in the shop manuals.An example procedure will be illustrated for an Oxygen sensor fault, P0130 whichindicates the sensor circuit malfunction. If you recall from the Oxygen sensor behaviordescribed earlier, the O 2 sensor switches between 0 (100 mv) and 1 volt (900 mv) asthe A/F mixture switches between the extreme conditions of lean and rich . Recall alsothat this voltage swing requires that the O must be at a temperature above 2 2000 C.The voltage of cold O 2 sensor is about 0.5 volt with a bias of 0.45 Volt and theelectronic control system will not go into closed-loop operation when O 2 is cold.Possible causes of fault code P0130 include:O 2 sensor is not functioning correctlyCircuit wiring is defective ( stuck at some value)The control (circuit) unit processing O 2 sensor signal is not functioning properlyFurther investigation is required to attempt to isolate the specific problem.To check the operation of the O 2 sensor , the average value of its output voltage is measuredusing the OBD II procedure which will be explained presently.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsThe desired voltage is displayed on the Instrument panel (IP) in multiples of 1/100 volt.Thus to say , “00” corresponds to 0 volts and “99” corresponds to 0.99 volt, etc.Using this voltage, the mechanic follows the following procedure: If the O sensor 2 voltageis less than 0.37volt and more than 0.57 volt, the mechanic is directed by the procedureto investigate the circuit wiring of the O 2 sensor for defects.If the O sensor 2 voltage is between 0.37 volt and 0.57 volt tests are performedto determine whether O sensor or the control (circuit) unit processing the O 2 2 sensor signalis faulty.The mechanic can then jumper the input leads together at the input to the control unit,simulating a O 2 sensor short circuit, and must read the sensor voltage value using theOBD II display procedure. If this voltage is less than 0.05 volt, the control unit isfunctioning correctly and the O 2 sensor must be investigated for defects. If the indicatedsensor voltage is greater than 0.05 volt, the control unit is faulty and should be replaced.when diagnosing a problem, the mechanic might wish to clear a fault code from the PCMmemory. A good reason to do this can be to test whether the failure is “hard” orintermittent. To clear DTC the mechanic pushes “OFF” and “HI” buttons on IPsimultaneously until “00” is displayed on IP.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsAfter all fault codes are cleared, the mechanic has several choices of test modes including:♦ Request current powertrain diagnostic data (mode $01)♦ Request current powertrain Freeze Frame” data (mode $02)♦ Request Emission related DTCs♦ Request OBD II test results of continuouslymonitored / non-continuously monitored systems♦ Request control of OBD II system.Mode $01: The purpose of this mode is to allow access to current emission related data values. The request forinformation includes a Parameter Identification(PID) value that indicates to OBD II the specific information requested.PID definition, scaling information, and display formats are included in SAE J 1979. for compliance.The OBD II module will respond to this message by transmitting the requested data value last determined by the PCM.All data values returned for sensor readings will be actual readings, not default or substitute values used by the PCMbecause of a fault with that sensor..Not all PIDs are applicable or supported by all systems. PID $00 is a bit encoded PID that indicates, for each module,which PIDs that module supports. PID $00 must be supported by all modules that respond to a Mode $01 request asdefined in the standard SAE J 1979, because tools that conform to SAE J 1978 use this request to determine the protocolinformation supported for OBD II communications.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsFor more detailed information on all the request modes that you can use to performOBD II diagnostics using OBD II communications, and Scan Tool (SAE J 1978) , refer tothe HS -3000 SAE standards manual.The powertrain control strategies to perform OBD II diagnostics in general are described so far.Now the specific diagnostics performed for DTCs of the sensors, actuators, and systemsindicated below will be briefly described.Manifold absolute pressure (MAP) sensor (DTCs(105 - 109): MAP sensor diagnostics areperformed for deterioration of piezoresister or capacitor characteristics. In case of electricalcircuit malfunction fault code 105 is assigned. If the sensor is indicating out of range reading faultcode 106 is assigned. If the sensor is indicating very low reading fault code 107 is assigned. If thesensor is indicating very high reading fault code 108 is assigned. The expected value is estimatedusing mass air flow sensor reading and engine parameters. If the tsensor is indicatingintermittent faulty reading, fault code 109 is assigned.Intake air temperature (IAT) sensor (DTCs(110-114):114): IAT sensor diagnostics are performed fordeterioration of thermister characteristics. In case of thermister circuit malfunction fault code 110is assigned. If the sensor is indicating out of range reading fault code 111 is assigned. Theexpected value is estimated using coolant temperature sensor reading rand engine parameters. Ifthe sensor is indicating very low reading fault code 112 is assigned. aIf the sensor is indicatingvery high reading fault code 113 is assigned. If the sensor is indicating intermittent faultyreading fault code 114 is assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsOxygen Sensor (O 2 ) Sensor ( DTCs 130-167):167): O 2sensor diagnostics areperformed to check deterioration of electrochemical pumping action thatgenerates voltage sensitivity to the oxygen density in the exhaustmanifold. In case of Zirconia electrode circuit malfunction fault code 130is assigned. If the O 2sensor is indicating slow response fault code 133 isassigned. The expected value is estimated using closed-loop loop frequencyand engine parameters. If the O 2sensor is indicating very low voltagefault code 131 is assigned. If the O 2sensor is indicating very highvoltage fault code 132 is assigned. If the O 2sensor is indicating noactivity, fault code 134 is assigned. In case of O 2sensor heater circuitmalfunction fault code 135 is assigned. The other codes from 135 5 to 167are assigned to similar faults for other O 2sensors and heaters in othercatalytic converters in the system. Oxygen sensor diagnostics are adescribed in detail in alter section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsMass air flow (MAF) sensor (DTC 100-104):104):MAF sensor diagnostics are performed for deterioration of electricalectricaland resister characteristics. In case of electrical circuit malfunctionmfault code 100 is assigned.If the sensor is indicating out of range 1reading fault code 1011isassigned. If the sensor is indicating very low reading fault code c102 isassigned. If the sensor is indicating very high reading fault code 103 isassigned. The expected value is estimated using MAP sensor readingand engine parameters. If the sensor is indicating intermittent ent faultyreading fault code 104 is assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsThrottle position Sensor (TPS) ( DTCs 120-124, 124, 220-229):229):TP sensor diagnostics are performed for deterioration of potentiometer tiometer operatedswitch A circuit characteristics. In case of switch A circuit malfunctionmfault code 120 is assigned. If the switch A circuit is indicating out of rangereading fault code 121 is assigned. If the switch A circuit is indicating very lowreading fault code 122 is assigned. If the switch A circuit is indicating very highreading fault code 123 is assigned. The expected value is estimated using air flowsensor reading and engine parameters. If the switch A circuit is indicatingintermittent faulty reading fault code 124 is assigned. For switch B circuit , faultcodes 220-224 224 are set for identical faults listed above. For switch C circuit cuit , faultcodes 225-229 229 are set for identical faults listed above.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsCrankshaft Angular Position Sensor ( DTCs 335-344, 344, 385- 389):Crankshaft angular position sensor diagnostics are performedfor deterioration of magnetic reluctance of sensor A circuitcharacteristics. In case of sensor A circuit malfunction faultcode 335 is assigned. If the sensor A circuit is indicating outoof range reading fault code 336 is assigned. If the sensor Acircuit is indicating very low reading fault code 337 is assigned. aIf the sensor A circuit is indicating very high readingfault code 338 is assigned. The expected value is estimatedusing engine speed another engine parameters.If the sensor A circuit is indicating intermittent faulty reading faultcode 339 is assigned. For sensor C circuit , faultcodes 34 0-3440are set for identical faults listed above.For sensor B circuit , fault codes 385-389 389 are set foridentical faults listed above.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEngine Coolant Temperature Sensor ( DTCs 115-119, 119, 125-126):126):Engine Coolant Temperature sensor diagnostics areperformed for deterioration of thermister characteristics. In case of thermisterand electrical circuit malfunction fault code 115 is assigned.If the sensor circuit is indicating out of range reading fault code 116 is assigned.If the sensor circuit is indicating very low reading fault code 117 is assigned. Ifthe sensor circuit is indicating very high reading fault code 118 is assigned.The expected value is estimated using engine parameters. If the tsensor circuitis indicating intermittent faulty reading fault code 119 is assigned. Forinsufficient coolant temperature for closed loop fuel control fault code 125 isassigned. For insufficient coolant temperature for stable operation fault code126 is assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsKnock Sensor ( DTCs 325-334):334): Knock sensor diagnostics areperformed for deterioration of piezoelectric or magneto restrictivecharacteristics. In case of electrical circuit malfunction fault t code 325 isassigned. If the sensor 1 circuit is indicating out of range readingfault code 326 is assigned. If the sensor 1 circuit is indicating very lowreading fault code 327 is assigned. If the sensor 1 circuit is indicatingvery high reading fault code 328 is assigned. Knocking is detected ected bythe oscillation frequency of the piezoelectric device or the voltagedeveloped by themagnetorestrictive device when knocking occurs. Ifthe sensor 1 circuit is indicating intermittent faulty reading g fault code329 is assigned.If the sensor 2 circuit is indicating same faults as listed above, fault codes330-3334 3334 are assigned to the respective faults. Knock sensor diagnosticsare described in detail in a later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEngine Speed Sensor ( DTCs 320-323):Engine speed sensor diagnostics are performed for eterioration ofmagnetic reluctance characteristics.In case of electrical circuit malfunction fault code 320 is assigned.If the sensor circuit is indicating out of range reading fault code 321 isassigned. If the sensor circuit is indicating no signal , fault code 322 isassigned. The expected value is estimated using engine parameters.If the sensor is indicating intermittent faulty reading, fault code 323 isassigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsVehicle Speed Sensor ( DTCs 500-503):Vehicle speed sensor diagnostics areperformed for deterioration of magnetic reluctance andelectrical characteristics. In case of electricalcircuit malfunction fault code 500 is assigned.If the sensor circuit is indicating out of range readingfault code 501 is assigned. If the sensor circuit isindicating very low reading fault code 502 isassigned. If the sensor is indicating very high/erratic/intermittent reading fault code 503 is assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsMisfire Detector( DTCs 300-312):Misfire sensor diagnostics areperformed for reduction of cylinder torque due to lack ofcombustion. In case of detecting misfire in cylinder 1fault code 300 is assigned. The fault codes for misfires incylinder 2 to 12 are similarly assigned to 301 - 312respectively. Misfire is described in detail in a later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEvaporative Emission control system (Purge flow) ( DTCs 465-469):469):Purge flow sensor circuit diagnostics are performed for deteriorationof Purge flow sensor circuit . In case of Purge flow sensor circuitmalfunction fault code 465 is assigned. If the Purge flow sensorcircuit is having range/performance problem purge flow fault code466 is assigned. If the Purge flow sensor circuit has detected a lowvalue, fault code 467 is assigned. If the Purge flow sensor circuithas detected a high value, fault code 468 is assigned. If the Purgeflow sensor circuit has intermittent fault, fault code 469 is assigned..

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEvaporative Emission control system (Purge valve) ( DTCs 440-445):445):Purge valve diagnostics are performed for deterioration of evaporative emissioncontrol system. In case of evaporative emission control system malfunction faultcode 440 is assigned. If the evaporative emission control system is havingincorrect purge flow due to faulty purge valve, fault code 441 is assigned. If theevaporative emission control system has detected small leak, fault fcode 442 isassigned. If the evaporative emission control system has purge control cvalvecircuit malfunction fault code 443 is assigned. If the evaporative ative emission controlsystem has purge control valve circuit open, fault code 444 is assigned. If theevaporative emission control system has purge control valve circuit shorted faultcode 445 is assigned. Evaporative system diagnostics are covered in detail in alater section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEvaporative Emission control system (Vent valve)( DTCs 446-449):449):If the evaporative emission control system vent control circuitmalfunction fault code 446 is assigned.If the evaporative emission control system vent control circuitopen, fault code 447 is assigned.If the evaporative emission control system vent control circuitshorted, fault code 448 is assigned.If the evaporative emission control system vent valve/solenoid circuitmalfunction, fault code 449 is assigned. Evaporative emission controlsystem diagnostics are described in detail in later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEvaporative Emission control system (Pressure sensor)( DTCs 450-455):455):If the evaporative emission control system pressure sensoris experiencing malfunction, fault code 450 is assigned.If the evaporative emission control system pressure sensorhas range/performance problem, fault code 451 is assigned.If the evaporative emission control system pressure sensorhas low input, fault code 452 is assigned.If the evaporative emission control system pressure sensorhas high input, fault code 453 is assigned.If the evaporative emission control system pressure sensoris experiencing intermittent fault, fault code 454 is assigned.If the evaporative emission control system pressure sensoris detected having leak, which is gross, fault code 455 is assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsIgnition Coil ( DTCs 350-379):379):Ignition coil diagnostics are performed for deterioration of ignition coilprimary/secondary characteristics. In case of ignition coil primary/secondary electricalcircuit malfunction, fault code 350 is assigned.In case of ignition coil A primary/secondary electrical circuit malfunction, fault code 351is assigned. Similarly for the case of ignition coil B to L primary/secondary electricalcircuit s' malfunction, fault codes 352-362 362 are assigned. If timing reference highresolution signal A has malfunction fault code 370 is assigned. If timing reference highresolution signal A has too many pulses fault code 371 is assigned.If timing reference high resolution signal A has too few pulses fault code 372 is assigned.If timing reference high resolution signal A has intermittent fault, ffault code 373 isassigned.If timing reference high resolution signal A has no pulses, fault t code 374 is assigned.If timing reference high resolution signal B has similar faults, fault codes 375-379379respectively are assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsFuel Trim Fuel system (fuel metering) ( DTCs 170-195, 195, 230-233 233 ):Fuel trim diagnostics are performed for deterioration of fuel trim values.In case of fuel trim malfunction (Bank 1)fault code 170 is assigned. If thefuel trim is indicating too lean system, fault code 171 is assigned. If thefuel trim is indicating too rich system fault code 172 is assigned.In case of fuel trim malfunction (Bank 2)fault code 173 is assigned. If thefuel trim is indicating too lean system, fault code 174 is assigned. If thefuel trim is indicating too rich system fault code 175 is assigned. Fueltrim diagnostics are described in detail in later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsIndividual Fuel Injectors ( DTCs 251-296):296):Injection pump fuel metering control circuit diagnostics areperformed for deterioration of fuel injection characteristics. In case of Injection pump fuelmetering control A (Cam/rotor/injector) malfunction, fault code 251 is assigned. In case ofInjection pump fuel metering control A (Cam/rotor/injector) range/performance problem,fault code 252 is assigned. In case of Injection pump fuel metering control A(Cam/rotor/injector) Low value, fault code 253 is assigned. In case of Injection pump fuelmetering control A (Cam/rotor/injector) high value, fault code 254 is assigned. In case ofInjection pump fuel metering control A (Cam/rotor/injector) intermittent fault, fault code255 is assigned. For control “B”faults similar to “A”, fault codes 256 to 260 are respectively assigned. afault codes 261-296 296 are assigned to injector coil circuits of cylinders 1 to 12 for low value, highvalue, and contribution/balance fault respectively.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsEGR Sensor /Valve ( DTCs 400-408):408):EGR sensor/ valve diagnostics areperformed for deterioration of exhaust gas flow characteristics. s. In caseof EGR flow malfunction fault code 400 is assigned. If the EGR R flow isindicating insufficient flow, fault code 401 is assigned. If the e EGR flowis indicating excessive flow, fault code 402 is assigned. If the EGRcircuit malfunction, fault code 403 is assigned. If the EGR circuit isindicating range/performance problem , fault code 404 is assigned.If the EGR sensor A circuit is indicating low value, fault code c405 isassigned. If the EGR sensor A circuit is indicating high value, fault code406 is assigned. Similar faults on sensor “B” circuit are assigned faultcodes 407, 408 respectively. EGR sensor/valve diagnostics aredescribed in detail in later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsIdle air control (IAC) valve 505-507507Idle control system diagnostics areperformed for deterioration of idle air flow characteristics. In case of idle aircontrol system malfunction fault code 505 is assigned. If the idle air controlsystem is indicating lower than expected flow, fault code 506 is assigned. Ifthe idle air control system is indicating higher than expected flow f,fault code507 is assigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsSecondary air injection system ( DTCs 410-419):419):Secondary air injection system diagnostics areperformed for deterioration of Secondary air injection system flow characteristics. In case ofSecondary air injection system malfunction, fault code 410 is assigned. aIn case of Secondary airinjection system incorrect flow, fault code 411 is assigned. In case of Secondary air injectionsystem switching valve A circuit open , fault code 413 is assigned.In case of Secondary air injection system switching valve A circuit shorted , fault code 414 isassigned. In case of Secondary air injection system switching valve B circuit malfunction, open ,or shorted, fault codes 415-417 417 are assigned respectively. In case of Secondary air injectionionsystem Relay A circuit malfunction , fault code 418 is assigned. In case of Secondary airinjection system Relay B circuit malfunction , fault code 419 is assigned.Secondary air injection system diagnostics are described in detail in later section.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsFuel level Sensor ( DTCs 460-464):464):Fuel level sensor circuit diagnostics are performed for deterioration of fuel levelsensor characteristics. In case of fuel level sensorcircuit malfunction fault code 460 is assigned. If thefuel level sensor circuit is indicating out of range/performance problem, faultcode 461 is assigned. If the fuel level sensor circuitis indicating very low reading, fault code 462 is assigned. If thefuel level sensor circuit is indicating very high reading fault t code 463 is assigned.The expected value is estimated using flow parameters. If thefuel level sensor circuit is indicating intermittent faulty reading, fault code 464 isassigned.

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsCatalytic converter ( DTCs 420-434):434):Catalyst system efficiency diagnostics are performed fordeterioration of characteristics, for Bank 1. In case of Catalystsystem efficiency below threshold, fault code 420 is assigned. Incase of Warm Up Catalyst efficiency below threshold, fault code421 is assigned. In case of Main Catalyst efficiency belowthreshold, fault code 422 is assigned. In case of Heated Catalystefficiency below threshold, fault code 423 is assigned. In case e ofHeated catalyst temperature, below threshold, fault code 424 isassigned. For identical faults for Bank2 , fault codes 430 to 434are respectively assigned. Catalytic converter diagnostics aredescribed in detail in later section.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsOBD II tests all sensors, actuators (valves) , switches, and wiring ing for proper connectivity,and checks the inputs and outputs of each device are within allowed range of values. Thefollowing sensors and actuators are tested and monitored by the OBD II diagnostics:Coolant temperature sensorIntake air temperature sensorManifold Absolute Pressure (MAP) sensorEngine Speed (Angular speed) sensorExhaust Gas Oxygen (EGO) sensorThrottle Position (Angle) (TPS) sensorCrankshaft (angular) Position sensorMass Air Flow (MAF) sensorKnock sensorIgnition timing sensorIgnition actuatorIdle air control (IAC) valveSecondary air valveEGR actuator (pintle(valve)Fuel metering actuatorFuel injector

Sensors and ActuatorsEmployed in OBD IIDiagnosticsEach sensor circuit listed below consists of mainly three parts:Sensor, A signal processor, and a display device.A Sensor converts the physical quantity such as temperature,pressure, vacuum, RPM,air flow, velocity, or acceleration into an electrical signal so thatit may beoperated by the signal processor

Sensors and ActuatorsEmployed in OBD IIDiagnosticsA signal processor performs some operation on theintermediate signal, to increase power level, reliability, andaccuracy. The signal is then manipulated into a form so thatwhen displayed, it can be understood by the viewer.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsThe display device converts the signal from signal processorinto a readable quantity.The sensor converts energy from the formof the measurement variable to an electrical signal. An idealanalog sensor generates an output voltage which isproportional to the quantity being measured:v 0 = Kq 0 , where K is the sensor calibration constant, v 0 isvoltage, and q 0 is the measured physical quantity, such astemperature, etc.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsK is the sensor Calibration constant whose units are volts perphysical quantity measured. An ideal sensor has a lineartransfer characteristic. Real sensorhas noisy transfer characteristic. As a consequence the sensoroutput needs signal processing which compensates for the noiseand transforms it, suitable for display.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsCoolant temperature sensor: Principle of operation: The sensor consists of athermister mounted in a housing which is designed to be inserted in the coolantolantstream. This housing is threaded with pipe threads which seal the e assembly againstcoolant leakage. A thermister is made of a semiconductor with a negativetemperature coefficient. The sensor is connected in an electrical circuit. see Figurein handout. The sensor output varies inversely with temperature.e.Diagnostics: The electrical characteristics of the thermister may deteriorate withtime. The reference voltage, and the series resister in the circuit are critical sourcesof variation from correct temperature. The relation between resistance andtemperature is not linear in thermister. Silicon temperature sensors provide amore linear output signal and are expected to replace thermister.OBD II DTCs : There are two failure modes. One is engine coolant temperaturenot correct, and other is insufficient temperature for closed-loop operation orunstable operation.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsIntake air temperature sensor Principle of operation:The sensor is similar in construction to the coolant temperature sensor. It is installedin the air intake manifold upstream of the air flow meter. The temperature vsvoltage across the thermister is not completely linear.Diagnostics: The electrical characteristics of the thermister may deteriorate withtime. The reference voltage, and the series resister in the circuit are critical sourcesof variation from correct temperature. The relation between resistance andtemperature is not linear in thermister. Silicon temperature sensors provide amore linear output signal and are expected to replace thermister.OBD II DTCs : There is one failure mode. It is intake air temperaturenot correct. OBD II DTC s are 110-114.

Sensors and ActuatorsEmployed in OBD IIDiagnostics :Manifold Absolute Pressure (MAP) sensor: Principle of operation: The sensor measures the theManifold Absolute Pressure (MAP) sensor:The sensor measures the thedisplacement of a diaphragm which is deflected by the manifold absolute apressure. There are two versions. Instrain gauge MAP sensor, the silicon diaphragm is sealed to a pyrex plate under vacuum. A set of sensingresistors is formed around the edge of this vacuum. The resistors s are formed by diffusing a “dopingimpurity” into the silicon. Manifold pressure applied to the diaphragm cause it to deflect which changes theresistance due to piezoresistivityproportional to the pressure. An electrical signal voltage, proportional ortional to the manifold pressure is obtained byconnecting the resistors in a Wheatstone bridge. In the second version vof MAP sensor, a film electrodeis deposited on the inside face of two alumina plates forming a capacitor. The capacitor capsule is placed in asealed housing which is connected to manifold pressure by a small l diameter tube. The deflection of theseplates when pressure is applied to them , causes their capacitance ce to change proportional to the appliedpressure. The capacitor is placed in an oscillator circuit. the frequency of oscillation is proportional to intaketemperature.Diagnostics The electrical characteristics of the strain gauge MAP sensor may deteriorate, resulting inincorrect output, stuck at low signal, stuck at high signal,, and intermittent failure.OBD II DTCsThe failure modes of MAP sensor are diagnosed by OBD II.DTCs for these faults are 105-109.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsEngine Speed (Angular speed) sensorPrinciple of operationThe sensor consists of a permanent magnet with a coil of wire wound around it.A steel disk with protruding tabs pass between the pole pieces of this magnet.The disk is mounted on the crankshaft. The number of tabs is half the number ofcylinders of the engine. The sensor is of magnetic reluctance type so that avoltage is generated with the frequency which is a multiple of revolutionsper minute (RPM) of the crankshaft. By measuring the frequency of thissignal voltage the engine RPM is calculated.DiagnosticsThe electrical characteristics of the magnetic reluctance sensor may deteriorate,resulting in incorrect output, stuck at low signal, stuck at high signal,,and intermittent failure..OBD II DTCsThe failure modes of Engine speed sensor are diagnosed by OBD II.DTCs for these faults are 320-323..

Sensors and ActuatorsEmployed in OBD IIDiagnosticsExhaust Gas Oxygen (EGO) sensorThere are two types of EGO sensors, both based on the use of oxides of materials.One uses Zirconia (ZrO 2 ), and the other uses titanium oxide (TiO 2 ). But ZrO 2is most popular and is described here. The sensor consists of ZrO 2 sandwichedbetween two platinum electrodes. One electrode is exposed to exhaust gasin the exhaust manifold, and the other electrode is exposed to normal nair forreference. The electrode that is exposed to exhaust gas is coated d with porous protectiveovercoat.The ZrO 2 attracts oxygen ions and they accumulate on theZrO 2 surface just inside platinum electrode. AS oxygen ions are negativelycharged, there will be a potential across the two electrodes if the oxygen ionson exhaust gas side are less than the oxygen ions on the normal air side. Thepolarity of this voltage is positive on the exhaust gas side and negative on air side.The voltage depends on the concentration of the oxygen in the exhaust gas and theEGO sensor temperature.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsEGO Oxygen sensor:Diagnostics: Check for abrupt change in voltage at stoichiometry. Must haverapid changes of output voltage in response to exhaust gas oxygen changes.Must have large difference in sensor output voltage between rich and leanA/F ratio conditions. Must have stable voltage with respect to exhausttemperature.OBD II DTCsThe failure modes of EGO sensor are diagnosed by OBD II.DTCs for these faults are 400-408..

DiagnosticsSensors and ActuatorsEmployed in OBD II6141DiagnosticsThrottle Position (Angle) (TPS) sensorPrinciple of operationThe sensor is a rotary potentiometer driven by the shaft of the butterfly valvein the throttle , and a linear potentiometer driven by the connecting rodbetween the accelerator pedal and the throttle. The sensor uses a continuousresistive film manufactured with thick film technique. The material is aceremet or resistive plastic compound. As the throttle butterfly valve rotatesthe potentiometer voltage varies in proportion to the angle of rotation ofthrottle.The electrical characteristics of the Throttle position sensor may deteriorate,resulting in incorrect output, out of range/performance values, stuck atlow signal, stuck at high signal,, and intermittent failure..OBD II DTCsThe failure modes of throttle sensor are diagnosed by OBD II.DTCs for these faults are 120-124.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsCrankshaft (angular) Position sensorPrinciple of operationThe crankshaft position sensor is similar in operation to engine e speedsensor.Diagnostics: The electrical characteristics of the Crankshaft position sensor may deteriorate,resulting in incorrect output, out of range/performance values, stuck atlow signal, stuck at high signal,, and intermittent failure..OBD II DTCsThe failure modes of crankshaft position sensorare diagnosed by OBD II.DTCs for these faults are 335-344.

Mass Air Flow (MAF) sensorSensors and ActuatorsEmployed in OBD IIDiagnosticsPrinciple of operation:The sensor consists of a hot film element (resistor) which is electrically heated to a constant temperature,that is measured by a temperature sensor. This element is incorporated in a whetstone bridge withpower supply from the output of an amplifier whose input is the differential voltage, of the bridgeresistors, which is balanced when there is no air flow over the hot film at constant temperature.When air flows over the film, the film cools and the resistance of the film element drops, causing bridgeunbalance thereby producing an input voltage to the amplifier. The output of the amplifier is connectedto the bridge circuit and provides power for the circuit. The amplifier voltage changes the resistance insuch a way as to maintain a fixed hot film temperature relative to the inlet temperature.The output voltage of the amplifier is a measure of the additional current required to heat the wire backto its original temperature. The additional current required is a measure of the heat transfer andtherefore of air mass flow rate. The second arm of the bridge is a similar self-heated wire, placed in stillair which provides compensation for changes in air temperature. and amplifier output voltage. Thisvoltage is converted to frequency which is measured by PCM using a counter. The counter value isproportional to the air flow rate (volume) from which the mass is computed by multiplying the volumeby the air density at that temperature.Diagnostics:The electrical characteristics of the Mass Air Flow sensor may deteriorate, resulting in incorrect output, outof range/performance values, stuck at low signal, stuck at high signal,, and intermittent failure..OBD II DTCs : The failure modes of crankshaft position sensor are diagnosed by OBD II. DTCs for these faults are 100-104.

Sensors and ActuatorsKnock sensorEmployed in OBD IIDiagnosticsPrinciple of operation The sensor measures the sudden risein cylinder pressure during combustion which commonly occurs with highmanifold pressure and excessive spark advance. The sensor consists sts ofmagnetorestrictive rods placed in a magnetic field of a coil. When excessive cylinderpressure is sensed the rods change the flux field in the coil which produces a voltagechange in the coil. The engine cylinder is mechanically resonant to the knockfrequency band, and the output signal is responsive to the first time derivative ofacceleration, also called jerk. The output signal of the sensor forms a closed loopsystem that retards the ignition to reduce the knock detected at the cylinders. Theproblem of detecting knock is complicated by the presence ofother vibrations and noise in the engine.Another version of knock sensor uses piezoelectric crystals, or the piezoresistance ofa doped silicon semiconductor.Diagnostics The electrical characteristics of the Knock sensor may deteriorate,resulting in incorrect output, out of range/performance values,stuck at low signal, stuck at high signal,, and intermittent failure.OBD II DTCs The failure modes of knock sensor are diagnosed by OBD II. DTCs for thesefaults are 325-329.

Ignition timing sensorSensors and ActuatorsEmployed in OBD IIDiagnosticsPrinciple of operation Wiegand-effect sensor ormagnetic reluctance sensor can be used to set ignition timing. In the latter type,a variable reluctance sensor is mounted on the engine block near a harmonic damper.A harmonic damper is a steel disk-shaped device connected to the crankshaftat the end opposite the flywheel. The damper has a notch cut in its outer surface. As anotch in the rotating damper passes by a variable reluctance sensor, the decrease inmagnetic flux generates a voltage pulse in the sensor circuit. This voltage pulse isused to set ignition timingDiagnosticsThe electrical characteristics of the Ignition timing sensor maydeteriorate, resulting in incorrect output, out of range/performancevalues, stuck at low signal, stuck at high signal,, and intermittentfailure.OBD II DTCs The failure modes of ignition timing sensor are diagnosed by OBD II. DTCs forthese faults are 350-379.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsIgnition actuator Principle of operationThe ignition actuator receives its control pulse from an ignition timing sensor.An ignition timing sensor measures the engine angular position to calculate theposition at which the spark should occur. The ignition timing sensor generates apulse that triggers an electronic circuit that in turn drives the coil primary. Thiscircuit, when so triggered, switches off the current in the coil primary, therebyinitiating the spark. The concept of an engine position sensor used as an ignitiontiming sensor is described previously.In another scheme, a permanent magnetcouples to a ferromagnetic element which mounted on the distributor shaft androtates with it. As this element rotates , the time varying magnetic field inducesa voltage in the coil that is proportional to the rate of change of magnetic field.Each time one of the cogs on the ferromagnetic wheel passes under the coil axis,one of the sawtooth-shaped pulses is generated. This wheel has one cog foreach cylinder , and the voltage pulses provide a timing pulse for calculating thespark time for the corresponding cylinder.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsDiagnosticsThe electrical characteristics of the Ignition actuator maydeteriorate, resulting in incorrect output, out of range/performancevalues, stuck at low signal, stuck at high signal,, and intermittentfailure.OBD II DTCsThe failure modes of ignition actuatorare diagnosed by OBD II. DTCs for these faults are 350-379.

Sensors and ActuatorsEmployed in OBD IIEGR actuatorDiagnosticsPrinciple of operationThe EGR actuator is a vacuum operateddiaphragm valve, with a spring that holds the valve closed if no vacuum is applied.The vacuum that operates the diaphragm is supplied by the intake manifold and iscontrolled by a solenoid operated valve under control of the PCM. When thesolenoid is energized by the PCM the EGR valve is opened by the applied vacuum.When the solenoid is deenergized the the vacuum is cut off from the EGR valve andthe spring holds the EGR valve closed. The amount of EGR is controlled by theduty cycle of the pulsed control current that is proportional to the average time ofenergized solenoid. The duty cycle, and the valve opening are properly controlledto ensure exact amount of EGR is provided without adversely affecting emissions.The duty cycle of the current pulse that energizes the solenoid ,Diagnostics and the EGR amount are correlated periodically by OBD IIdiagnostics.OBD II DTCs The failure modes of EGR flow are diagnosed by OBD II. DTCs for these faultsare 400-408.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsIdle air control (IAC) valve Principle of operationThe valve is an electronicallycontrolled throttle bypass valve which allows air to flow around the throttle plate(which is closed due to low engine RPM and vehicle being stationary) and produces thesame effect as if the throttle is slightly opened. A stepper motor opens the pintle (valveallowing a limited amount of air to bypass the closed throttle plate. The steppermotor controls the pintle movement accurately thus controlling the amount ofbypass opening into the intake manifold. The duty cycle of the stepper motoris controlled by the PCM which monitors the pintle position and commands thestepper motor to move back the pintle to open the bypass by the calculatedamount and move the pintle forward to close the bypass at the end of the duty cycle.DiagnosticsOBD II DTCsThe duty cycle of the stepper motor , and the amount of bypass by thepintle valve are correlated periodically by OBD IIdiagnostics. The initial position and the final position of the pintlevalve are continuously checked.The failure modes of idle air flow are diagnosed by OBD II. DTCs for thesefaults are 505-507.

Secondary air valvesSensors and ActuatorsEmployed in OBD IIDiagnosticsPrinciple of operation:The secondary air is controlled by twosolenoid valves similar to the EGR valve. One valve switches airflow to the exhaustsystem or to outside air cleaner. The other valve switches air flow to theexhaust manifold or to the second chamber of the three-way catalytic converter.The air routing is done by the PCM based on engine coolant temperature, andA/F ratio. During cold start the secondary air goes to exhaust manifold, and duringclosed loop operation, secondary air goes into catalytic converter. During heavyloads and during severe deceleration, secondary air is directed to air cleaner whereit has no effect on exhaust temperature.Diagnostics The duty cycle of the current pulse that energizes the solenoid ,and the secondary air flow are correlated periodically by OBD IIdiagnostics.OBD II DTCsThe failure modes of secondary air flow are diagnosed by OBD II.DTCs for these faults are 410-419.

DiagnosticsOBD II DTCsfaults are 170-175.Sensors and ActuatorsEmployed in OBD IIDiagnosticsFuel metering actuatorPrinciple of operation The actuator used for electroniccontrol of fuel metering is the throttle body fuel injector. The TBFI consists of oneor two solenoid-operated fuel injectors that are mounted in a housing on the intakemanifold. The fuel is injected into and atomized by the moving air stream that flowsinto the intake manifold. PCM controls the amount of fuel. Fuel metering actuatordelivers fuel in precise amounts under PCM control. The amount of fuel injected intothe cylinder is determined by the length of time that the injectors are energized which istheir duty cycle. The injection time is synchronous with engine speed and is given by:intake air amount/engine speed x compensation coefficient (correction factor) +voltage-compensated injection time. Fuel trim is used to find the correction factor.Compensation coefficients are dependent on driving conditions such as heavy load,idle, or braking. Asynchronous injection is performed during start-up andacceleration. Fuel injectors are based on multipoint injection in which each eachinjector is mounted on the intake manifold of its cylinder.PCM monitors the rate of updating fuel trim and the correction factorto determine if the fuel metering actuator (and injectors ) is functioningproperlyThe failure modes of fuel system are diagnosed by OBD II. DTCs for these

Sensors and ActuatorsEmployed in OBD IIFuel injectorDiagnosticsPrinciple of operationIndividual fuel injectors locatedin the intake manifold near the intake valve is the current practice. Each fuel injectoris a solenoid activated plunger which is normally closed inhibiting fuel delivery.Whenactivated, the valve opens and a predetermined quantity of fuel is sprayed into theair flowing into the cylinder and mixed with this air. This valve opening is timedrelative to the intake stroke by the PCM controller.The fuel injector consists of a spray nozzle and a solenoid operated plunger. Wheneverthe plunger is lifted from the nozzle, fuel flows at a fixed rate through the nozzle intothe air stream going to the intake manifold. The plunger acts as a fuel injection on-offvalve. The plunger position is controlled by a solenoid and a spring. When no currentis applied to the solenoid, the plunger is tightly held against the nozzle by a spring.The plunger is pulled away from the nozzle when the solenoid is activated, causingfuel to flow which is under pressure. The solenoid, plunger, and nozzle act as anelectrically switched valve, which is closed or open, depending on whether thethe control current is off or on respectively. The fuel flow rate is regulated by fuelpressure and nozzle geometry. The amount of fuel is proportional to the time the valveis open. The control current that operates the fuel injector is pulsed on and off, and theAir/Fuel ratio is proportional to the duty cycle of the pulse train from the PCMcontroller.

Sensors and ActuatorsEmployed in OBD IIDiagnosticsDiagnosticsOBD II DTCsThe duty cycle of the current pulse that energizes the solenoid ,and the fuel amount are correlated periodically by OBD IIdiagnostics.The failure modes of fuel injector are diagnosed by OBD II. DTCs for these faultsare 251-296.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPowertrain Control Module (PCM) performs the following functions in relation toOBD II Diagnostics:Perform microprocessor-based self diagnostics to ensurecorrect operation of the PCM and safe storage ofOBD II diagnostic data in memory.Perform On-Board diagnostics in real time and alert thedriver by illuminating MIL in case of a faultPerform powertrain control functions to reduce emissionsand meet OBD II regulations during open-loopoperation at start-up time.Perform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop controlduring normal operation.

Functionality of PowertrainControl Module (PCM) inOBD IIPerform microprocessor-based self diagnostics to ensure correct operationof the PCM and safe storage of OBD II diagnostic data in memory.The PCM performs the following self diagnostics:Verify the checksum of the program memory in ROM with its function andcorrect version.Perform read and write test of RAM cells for fault free memoryPerform processor functions in CPU, peripheral devices including A/Dconverters, watchdog timers, and registers to verify that the processor isfunctioning properly.Perform checks on stored vehicle data and verify that thedata is not corrupted and is within reasonable limits of vehicle e operation.

Functionality of PowertrainControl Module (PCM) inOBD IIPerform On-Board diagnostics in real time and alert the driver by illuminatingingMIL in case of a fault . The PCM performs on-board diagnostics in real timeby interspersing diagnostics with vehicle control functions. The diagnosticsare classified into priority levels from 1 to 8 or 9. The highest priority level tests aredone every 1 millisecond, followed by next priority level tests every 5 milliseconds,10 milliseconds, 20 milliseconds, 50 milliseconds, 100 milliseconds, 200 milliseconds,500 milliseconds, and 1 second. The highest priority level tests are those thateffect safety and emissions to a high degree according to OBD II regulations.These include Oxygen sensor (lambda sensor) , and fuel trim checks duringclosed loop operation of the vehicle. The next priority checks are the interrupttimers, and watchdog timers. The next priority tests are sensors, including EGOsensor, Throttle position sensor, Misfire detection, MAP sensor, Engine RPM sensor,MAF sensor, Crankshaft position sensor, and Engine coolant sensor.The next priority tests are EGR intrusive tests, Catalytic converter's secondary air,and canister purge, fuel level sensor, pedal actuator, and ignition timer.The next priority checks are periodic self tests.

Functionality of PowertrainControl Module (PCM) inOBD II OBD IIThe PCM is interrupted by the real time scheduler during the performance ofits normal vehicle control functions when the on-board tests are due. At this time thePCM saves its current state of the vehicle and performs the diagnostics. Thistakes about 100 microseconds. Then the PCM returns to its normal vehiclecontrol functions. This repeats for each priority level diagnostics. In thismanner the PCM spends about 15- 40% of its time to diagnostics and the rest toperform its normal vehicle control functions. The method of testing each componentdepends on the electrical characteristics and vehicle functions performed by thedevice. The PCM maintains the low and high limits for each test parameter, andnormal range of values and performance requirements for each component that ittests. The PCM also has adequate hardware test capability to find a short circuit,or open circuit, or the noise level of a signal, including battery, power supply, wiringharness, each sensor, actuator and control unit related to emissions control.The PCM tests each sensor by measuring each test parameter, such as input, or outputand comparing it with the expected value stored in the technical data for the sensor.

Functionality of PowertrainControl Module (PCM) inOBD II OBD IIThe PCM also compares the signals of the components under test with acombination of information provided by other sensors, to verify thereasonableness of values provided by the components. The noise level and theperformance of each signal of the component is checked as well. Actuators aretested similarly to the way the sensors are tested for short circuit, open circuit, andrange and performance levels. The test method also includes computing a testoutput of a sensor using different engine parameters and comparing them forcompliance. This is called analytical redundancy. The actuator under certainconditions is intrusively activated and its output is measured to verify against theexpected value for proper operation. If discrepancies to the nominal values arediagnosed in any component under test , the information is stored in memorywith all the relevant supporting data, such as engine speed, MAP sensor, coolanttemperature, and others. This is called “Freeze Frame” since it gives the vehicle’sstate at the instant of failure of that component.. Thus defects that appearance orunder certain conditions can be diagnosed. If the fault occurs only once duringseveral cycles, it is deleted.

Functionality of PowertrainControl Module (PCM) inOBD II OBD IIIf the fault persists for two cycles consecutively, it is not erased until the defectis repaired by the technician. In case of an out of range output of a sensor , thePCM substitutes a corresponding reasonable value for that vehicle conditionof operation. The PCM also provides clear information to the driver byilluminating the MIL (Malfunction Indicator Light) in case of a defect withoutcausing alarm for minor problems. All relevant data for off-board diagnostics,and repair are stored by the PCM in its memory for later use. In the case of adefect that completely impairs the vehicle performance the PCM has the fullcapability to switch the vehicle state to a safe state of lesser capability called“Limp Home” state, in which the vehicle is brought to a safe degraded operatingcondition, that includes a halt of the vehicle. The PCM communicates with theOBD II scan tool and provides diagnostic data, and OBD II DTCs of all faultsexperienced by the vehicle so far to the external tester to facilitate off-boarddiagnostics, and vehicle repair. In this respect OBD II provides SAE J 1850 datalink for communication of diagnostic data, SAE J 2012 provides the DTC messageformats, and SAE J 1979 provides the test modes, requesting PCM for emissionsrelated powertrain diagnostics data.

Functionality of PowertrainControl Module (PCM) inOBD II OBD IIOBD II Functions: These include catalyst monitoring, misfire monitoring,evaporative system monitoring, secondary air system monitoring, fuel systemmonitoring, oxygen sensor, monitoring, EGR (exhaust gas recirculation) systemmonitoring, and comprehensive component monitoring.Catalyst: PCM shall individually monitor the front catalyst or catalysts whichreceive untreated engine out exhaust gas for malfunction. This is done bymonitoring the oxygen sensor in front of the catalyst. In addition the PCMshall monitor the oxygen sensor situated down stream of the catalyst, and comparethe signals of the two sensors to verify that the catalysts are functioning properly.A properly functioning catalyst shows a storage effect such that the oscillationsof the lambda oxygen sensor at the down stream of the catalyst are minimal orzero, while the upstream oxygen sensor is oscillating with amplitude and frequencyof the limit cycle of the rich/lean, air /fuel mixture.Misfire Detection: The PCM shall monitor engine misfire and identify cylinderexperiencing misfire. If a certain percentage of misfires within 200 or 1000 revolutionsis detected, a fault code is stored by the PCM and the MIL is illuminated by the PCM.Misfire detection is critical to emissions and is described in detail in a later section.

Functionality of PowertrainControl Module (PCM) inOBD IIOxygen sensor: The PCM shall monitor the output voltage, the response rate, andother parameters that can affect emissions, and all fuel control oxygen sensors formalfunction. The algorithm involves monitoring for short circuit, or breaks, andmonitoring the switching frequency of the closed-loop control. If this is too slowor too fast relative to the limit cycle frequency of the air/fuel mixture, then theoxygen sensor is deemed defective. The PCM illuminates the MIL in the event of afault and stores the DTC and diagnostic data in memory. Heated sensors aremonitored using heater current, voltage, and sensor temperature .Evaporative system: The PCM shall control the air flow of the complete evaporativesystem. The PCM shall also monitor the emission of HC vapors into the atmosphereby performing a pressure check and a vacuum check of the purge valve,and the canister valve, using intrusive purge operations. The algorithm is two fold.At idle position, the purge valve is activated and the lambda sensor is monitoredfor its reaction which should indicate a rich reading (high voltage of 900 mv). For leakdetection of the evaporative system, the canister valve is closed, and the canister pressure isdecreased to about about -1.5 KPa. Then the complete system is turned off and the pressurewithin the canister is monitored for variation with time. The pressure gradient, together withother parameters like the amount of fuel, may indicate a leak. If the leak persists for twoconsecutive cycles, the MIL is illuminated.

Functionality of PowertrainControl Module (PCM) inOBD IISecondary Air system: The PCM shall monitor the secondary air delivery systemand proper functioning of the air switching valves. The algorithm consists inmonitoring the lambda sensor for correlated deviations when the secondary airflow is changed from exhaust manifold or to catalyst chamber or to outside aircleaner.Fuel system: The PCM shall monitor the fuel delivery system. The algorithm is tomonitor the deviations of the stoichiometric ratio which last for a longer time andstore them within the adaptive mixture controller consisting of short term fuel trim,and long term block learn. If these values exceed defined limits, components of thefuel system are deemed defective. This will result in illuminating the MIL andstoring the DTC in memory.Exhaust Gas Recirculation (EGR) system: The PCM shall monitor the EGR systemfor low and high flow rate malfunctions. The algorithm is two fold: At overrun, thefuel is cut off and the EGR valve is completely opened. The flow of exhaust gas tothe intake manifold raises the manifold pressure, which is recorded. Secondlymonitor the increase of he manifold intake temperature when the EGR valve isopened.

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations during open-loop operation at start-up time.The primary function of the PCM is to control the powertrain operation duringthe start up and during the warm up conditions. In both the conditions, theprimary function of the PCM is to maintain the Air/Fuel ratio at or nearstoichiometry. The modes in which this control is accomplished are :open-loop control and closed-loop control corresponding to start up andwarm up condition respectively. In this section,we consider the open-loop control and in the next section we will describe theclosed-loop control by the PCM.The open-loop control by the PCM is in effect during the start up of the vehiclewhen the electronic fuel control system is not controlled by the lambdaoxygen sensor due to its low temperature (below 300 C). During this mode thePCM controls the fuel system to remain in stoichiometry by using MAP, Engine RPM,EGR and Coolant temperature sensor in stead of the lambda oxygen sensor.

Functionality of PowertrainControl Module (PCM) inOBD IIThe PCM obtains the mass air flow from the MAF sensor and obtains the massfuel required to keep the air/fuel ratio equal to stoichiometry (14.7) from lookuptables. The inputs to the lookup table is MAP, Engine RPM, Coolant temperature,and EGR, all of which are readily available by computation, or lookup table.The value of the speed density product R a *d a is given by:R a = (Engine RPM/60) * ( Engine displacement/2)* volumetric efficiency - EGR volume flow rated a = M a / R a , where M a is the mass of air, and R a is the volume at in take air temperature T.Tables of d a , the density of air measured versus temperature are available in lookup tables.Engine displacement and volumetric efficiency are engine design parameters, which areconstant. Lookup tables with inputs: Engine RPM, MAP, T, and EGR give directly themass flow rate of air, which is product R a *d a . This is used as input into another lookuptable that gives the duty cycle of the fuel injector, which gives the amount of fuel required tokeep the A/F mixture at stoichiometry. This lookup is performed by the PCM to complywith OBD II regulation mandated by CARB and EPA for controlling emissions..

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop controlduring normal operation.Closed-loop mode of control is selected by PCM when the lambda sensor hasattained a temperature more than 300 0 C. The intake Air/Fuel ratio iscontrolled in a closed loop by measuring the EGO at the exhaust manifoldand altering the input fuel flow rate with fuel injector to correct for a rich orlean mixture indication. The PCM continuously adjusts the output signal tothe fuel injector to maintain stoichiometry by varying the duty cycle. Variationsin engine transport delay with RPM are corrected by reducing the cyclefrequency and duty cycle ramp rate with decreasing RPM. The fuel flow iscorrected by using fuel trim correction using short term update and longterm update scheme, to compensate for the engine performance over time.

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop control.Acceleration Enrichment: When heavy load is demanded by the driver, thePCM adjusts the fuel control to provide enriched air/fuel mixture to maximizeengine torque and neglect emission control. This is for short time and isapproved by EPA. The PCM performs this by detecting high throttling anglesensor voltage or high MAP sensor value. In case WOT, the PCM increases theduty cycle of the fuel injector to the maximum allowed value, which may resultin A/F ratio of as low as 12:1.

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Deceleration Enleanment and Idle Speed Control: When the driverdecelerates the vehicle very hard, the PCM reduces the engine torque bycutting off fuel , with decel fuel cut off mode in which the fuel injector isturned off or the duty cycle is drastically reduced. A typical algorithm forfuel injection duration for the desired Air/Fuel ratio of stoichiometry is given by:T = base pulse width from lookup table for mass air flow + closed loopcorrection factor closed loop correction factor is the fuel trim block learn valuealluded earlier.For open-loop control , closed-loop correction factor is zero.For closed-loop operation, correction factor, C, is given by:C = I*A + B*F, where A and B are constants, and I is the integral part, and F isthe fractional part of the correction factor..

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations.I and F are determined from the fuel trim, and EGO sensor. When EGO indicatesrich mixture , Fuel trim value I is reduced by 1, and increased by 1 for lean mixture.The base pulse width of fuel injector is proportional to mass air flow given by:T = K* R a, where factor K is determined by the PCM, depending on the Mode offuel control. For closed-loop normal operation, K corresponds to stoichiometricAir/Fuel mixture. For cold start, K corresponds to A/F = 12:1. For deceleration, K=0.The mass air flow is calculated by the PCM as described before.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Idle Speed Control: When the throttle angle reaches its closed positionand engine RPM falls below a preset value (about 600), the PCM switchesto idle speed control mode. The PCM controls the idle air controlpintle (valve) to let air to flow into intake manifold, bypassing the closedthrottle to prevent the engine from stalling due to lack of torque. Thepintle is operated by a stepper motor, which withdraws the pintle from itsclosed position (seat) to open the bypass that lets a limited amount ofair flow into the intake manifold. Idle speed is detected by the RPM sensorindicating a low value, the vehicle is stationary, and throttle is closed. ThePCM adjusts the pintle to keep the idle speed around 600 to 700 RPM. Thepintle valve is completely closed when engine is not idling.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop control.EGR Control: At high engine load (high throttle angle), and high Engine RPM,and at high engine coolant temperature, the cylinder temperature at combustionreaches temperature greater than 3000 0 F which causes NOx emissions to increasebeyond the OBD II limits. For this reason, the PCM recirculates a small portion ofthe exhaust gases into the intake manifold. This has the effect of reducing oxygencontent without reducing the mass of gas processed. The combustion impartsenergy to the inert exhausts gas as well as to the air charge. The net effect isto retain much of the engine power while reducing the flame temperatureat part load, thus decreasing production of NOx. The PCM controls the EGRvalve depending on the throttle angle, engine RPM, coolant temperature. EGR iscompletely closed during cold start and during start up of the engine.The duty cycle of the EGR valve is obtained from predefined table lookup.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop control.EGR Control (contd) : The EGR signal can either control a valve opening, which isdetected by a valve position sensor, or the PCM can meter the exhaust gasin the same way as the PCM meters the fuel in the fuel injector. The PCM usesthe sensor similar to throttle position sensor to determine the amount of EGRfed into the air intake during open loop control mode, to make air/fuel ratiocalculation, when it is not stoichiometric ratio. This sensor gives an electrical signalwhich is proportional to the amount of opening of the EGR valve that can beused to compute the amount of EGR from the knowledge of the valve’s duty cycle.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Secondary Air management: The PCM controls the powertrain operation inengine warm-up mode by selecting a warm-up time from a table lookuptable based on the coolant temperature. During engine warm-up the Air/Fuelratio is still rich as in during engine crank, when the engine is still cold. The PCMcontrols the powertrain functions in open-loop mode and uses secondary airmanagement to bring up the converter temperature as well as EGO sensortemperature, to go into closed-loop mode as soon as possible when the emissionsare lowest and meet OBD II requirements. The PCM provides extra oxygen rich airto either the converter itself, or to the exhaust manifold. The catalyst temperaturemust be above 200 0 C to efficiently oxidize HC and CO and reduce NOx to N 2.During warm-up when the catalytic converter is cold, the HC , and CO are oxidizedin the exhaust manifold. This creates extra heat to speed warm-up of the converter,and EGO sensor, enabling the PCM to go into closed-loop control.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Secondary Air management (contd): The converter can be damaged if too muchheat is applied to it. This can occur if large amounts of HC and CO are oxidized inexhaust manifold during heavy loads which call for fuel enrichment or duringsevere deceleration. In such cases, the PCM directs the secondary air to the aircleaner where it has no effect on exhaust temperature.After warm-up, the main use of secondary air is to provide an oxygen rich air to thesecond chamber of the three-way catalyst, dual-chamber converter system. In thedual chamber converter, the first chamber contains rhodium, and platinum toreduce NOx and to oxidize HC and CO. The second chamber contains only platinumand palladium.. The extra oxygen from the secondary air improves the ability of theconverter to oxidize the HC and CO in the second converter chamber. The PCMcontrols the secondary air using two solenoid valves similar to EGR valve.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Secondary Air management (contd): The first solenoid valve switches air flow to theair cleaner or to the exhaust system. The second solenoid valve switches air flow eitherto the exhaust manifold or to the catalytic converter. The PCM controls the air flowdepending on the engine coolant temperature, and Air/Fuel ratio which is notstoichiometric ratio in this mode, which is open-loop control.Evaporative Emission Canister Purge: The PCM releases the collected fuelfuel vapors in the canister into the intake manifold via a solenoid controlled purgevalve periodically, during closed loop operation. This will simplify fuel calculationduring open-loop control.

Functionality of PowertrainControl Module (PCM) inOBD II DiagnosticsPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Automatic system Adjustment:: The PCM during closed-loop mode of controlchecks the open-loop calculated air/fuel ratios and compares them withclosed-loop average limit values which are the ideal values for minimumemissions. If the difference is large, the PCM corrects the open-loop lookuptable values so that the open-loop values are in close agreement with theclosed-loop values. This updated open-loop lookup table is stored innon-volatile RAM memory. When the engine is started next time the PCMuses the new lookup values which are closer to the stoichiometric ratio.This feature is important since it enables the PCM to adjust to long-term changesin engine and fuel system conditions due to wear and usage. This is similarto fuel trim algorithm for fuel injection control.These are all the PCM control functions performed to reduce emissionsand comply with OBD II requirements.