Introduction to On Board Diagnostics (II)

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.