Fuel System Monitor

To comply with clean air regulations, vehicles are equipped with catalytic converters. These converters reduce emission of hydrocarbons, oxides of nitrogen and carbon monoxide. The catalyst works best when air/fuel (A/F) ratio is at or near optimum of 14.7:1.

The PCM is programmed to maintain optimum air/fuel ratio. This is done by making short term corrections in fuel injector pulse width based on O2S output. The programmed memory acts as a self calibration tool that engine controller uses to compensate for variations in engine specifications, sensor tolerances and engine fatigue over life span of engine. By monitoring actual air/fuel ratio with O2S (short term) and multiplying that with program long-term (adaptive) memory and comparing that to limit, it can be determined whether it will pass an emissions test. If a malfunction occurs such that PCM cannot maintain optimum A/F ratio, then MIL will be illuminated.