To comply with clean air regulations, DaimlerChrysler vehicles are equipped with catalytic converters that reduce the amount of HC, CO and NOx emissions released from the vehicle. The catalyst works best when the A/F ratio is at or near an optimum value of 14.7:1. The PCM is programmed to maintain this optimum A/F ratio.
This is accomplished by making Short Term fuel trim corrections in injector pulse width based upon the O2 Sensor input. The programmed memory in the PCM acts as a self-calibration tool to compensate for variations in engine specifications, sensor tolerances and engine fatigue over the life span of the engine.As injector pulse width increases, the amount of fuel delivered by the fuel injector is increased. A shorter pulse width decreases the amount of fuel delivered. The PCM monitors engine load, RPM, TP Sensor, ECT Sensor signals in order to make changes to injector pulse width.