Circuit Description

The powertrain control module (PCM) times the intervals between each pulse of the crankshaft position sensor and compares each time interval with the other 8 to determine when an excessive change in crankshaft speed has occurred. This pulse is generated from a reluctor wheel located on the front of the crankshaft. If the crankshaft speed is less than an expected amount, the PCM will increase the amount of fuel needed to correct the misfire. If the amount of fuel exceeds the calibrated value, the PCM will interpret this as a misfire and set the diagnostic trouble code (DTC). The misfire diagnostic is used only to identify a weak cylinder needing additional fuel.