Introduction to On Board Diagnostics (II)

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.