Catalyst Damaging:: Notes

During an interval of 200 crankshaft revolutions the misfire events of all cylinders are added and if the sum is greater than a predetermined value a fault will be set identifying the particular cylinders(s). The "Service Engine Soon" lamp:

• On vehicles with a Siemens Control Module (M54 engines) - the lamp will immediately go to a steady illumination since fuel to the injector(s) is removed. Fuel cut-off to the cylinder will resume after several ( << 7) periods of decel if crankshaft sensor adaptation is successfully completed or the engine is shut-off and restarted.

In each case the number of misfire events permitted is dependent on engine speed, load and temperature map.

The process of misfire detection continues well after the diagnostic drive cycle requirements have been completed. Misfire detection is an on-going monitoring process  that is only discontinued under certain conditions.