Introduction to On Board Diagnostics (II)

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.