Misfire Monitor: Notes

The input to the Misfire Monitor is the signal from the crankshaft position sensor and timing wheel. The signal is acquired and processed by the PCM and provided to the Misfire Monitor as individual tooth period measurements. The Monitor uses the tooth period measurements to calculate crankshaft acceleration signals for misfire detection. All misfire processing is performed in software (separate chips are no longer used except for some vehicle lines that may still be using older style PCMs.)

Two different technologies are used for misfire monitoring. They are the Low Data Rate (LDR), and High Data Rate (HDR) systems. The LDR system is capable of meeting the FTP monitoring requirements on most engines and is capable of meeting "full-range" 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 "full-range" misfire monitoring requirements on 8 and 10 cylinder engines.

All software allows for detection of any misfires that occur 6 engine revolutions after initially cranking the engine. This meets the OBD-II requirement to identify misfires within 2 engine revolutions after engine start/restart (> 150 rpm below warm idle speed) for conventional and stop-start vehicles and 2 engine revolutions after engine fueling begins for engine start/restart for hybrid vehicles.

The Monitor includes a diagnostic check on the crank sensor input. The Monitor checks the number of tooth period measurements received on each cylinder event. A P1336 will be set if the Monitor receives an invalid number of tooth period measurements. A P1336 points to noise present on the crank sensor input or a lack of synchronization between the cam and crank sensors.