Introduction to On Board Diagnostics (II)

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations in closed-loop loop controlduring normal operation.Closed-loop mode of control is selected by PCM when the lambda sensor hasattained a temperature more than 300 0 C. The intake Air/Fuel ratio iscontrolled in a closed loop by measuring the EGO at the exhaust manifoldand altering the input fuel flow rate with fuel injector to correct for a rich orlean mixture indication. The PCM continuously adjusts the output signal tothe fuel injector to maintain stoichiometry by varying the duty cycle. Variationsin engine transport delay with RPM are corrected by reducing the cyclefrequency and duty cycle ramp rate with decreasing RPM. The fuel flow iscorrected by using fuel trim correction using short term update and longterm update scheme, to compensate for the engine performance over time.