Misfire Monitor Operation

The signal from the crankshaft position sensor and timing wheel is processed by the PCM into individual tooth period measurements and provided to the misfire monitor. The misfire monitor uses the tooth period measurements to calculate crankshaft acceleration signals for misfire detection.

A low data rate (LDR) and high data rate (HDR) are the 2 different types of misfire monitoring systems used. The LDR system is capable of meeting the federal test procedure monitoring requirements on most engines and is capable of meeting the full range of misfire monitoring requirements on 3 and 4 cylinder engines. It is also used on 6 cylinder engines with rear mounted crank sensors. The HDR system is capable of meeting the full range of misfire monitoring requirements on 8 cylinder and 10 cylinder engines. The HDR system on these engines meets the full range of misfire phase-in requirements specified in the on board diagnostic (OBD) regulations. The PCM software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the OBD requirement to identify misfires within 2 engine revolutions after exceeding the warm drive, idle RPM.

The monitor includes a diagnostic check on the crank sensor input that checks the number of tooth period measurements received on each cylinder event. If the monitor receives an invalid number of tooth period measurements, DTC P1336 will set. This DTC indicates that noise is present on the crank sensor input or there is a lack of synchronization between the camshaft and crankshaft sensors.