Introduction to On Board Diagnostics (II)

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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..
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Introduction to On BoardDiagnostics
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OBD II monitors more components and
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Powertrain and EmissionControls in
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Powertrain and EmissionControl in P
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OBD II for L & MD VehiclesSTD Manua
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OBD II for L & MD VehiclesDiagnosti
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Introduction to On Board Diagnostics (II)

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