Introduction to On Board Diagnostics (II)

Functionality of PowertrainControl Module (PCM) inOBD IIPerform powertrain control functions to reduce emissionsand meet OBD II regulations.Deceleration Enleanment and Idle Speed Control: When the driverdecelerates the vehicle very hard, the PCM reduces the engine torque bycutting off fuel , with decel fuel cut off mode in which the fuel injector isturned off or the duty cycle is drastically reduced. A typical algorithm forfuel injection duration for the desired Air/Fuel ratio of stoichiometry is given by:T = base pulse width from lookup table for mass air flow + closed loopcorrection factor closed loop correction factor is the fuel trim block learn valuealluded earlier.For open-loop control , closed-loop correction factor is zero.For closed-loop operation, correction factor, C, is given by:C = I*A + B*F, where A and B are constants, and I is the integral part, and F isthe fractional part of the correction factor..