Spark Timing Monitor: Notes

The powertrain control module (PCM) is equipped with a spark conduction capture circuit which measures the timing and duration of the spark delivered by processing the flyback voltage signal from the primary side of the ignition coil. With the cold start emission reduction monitor enabled, the spark control strategy requests retarded spark timing. While retarded spark timing is requested, the spark timing monitor compares the measured spark timing from the spark conduction capture circuit to the commanded spark timing from the spark control strategy. For the purpose of detecting spark timing failures, the spark timing monitor increments a fault filter if the measured spark timing is advanced by more than 5 degrees from the commanded spark timing. A failure is indicated if the fault filter exceeds a value of 200, equivalent to a failure duration of approximately 4 seconds.