Misfire Monitor Diagnosis

Misfire Monitor Diagnostic Tests

When the engine is running and a cylinder misfires the crankshaft slows down momentarily. The control module has the ability to detect this change in speed by monitoring the input signals from the following sensors:

^ The Crankshaft Position (CKP) sensor

^ The Camshaft Position (CMP) sensor.

When the control module is running the misfire on-board diagnostic tests and a misfire is detected the misfire counter stores (accumulates) the position and the number of misfires. Two counters (accumulators) are assigned to each of the cylinders. The counters are as follows:

^ The Current Misfire Counters. The current misfire counters store the number misfires that have occurred in the last 200 engine cycles. When the control module detects a unacceptable amount of misfires stored in a current misfire counter the misfire on-board diagnostic test fails and a misfire DTC will set.

^ The History Misfire Counters. When a misfire DTC is set, the history misfire counters store the total number of misfires that have occurred every 200 engine cycles.