Introduction to On Board Diagnostics (II)

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.