Ignition Control Module (ICM)

The ICM receives an 18X pulse from the CKP sensor 1 signal circuit and a 3X pulse from the CKP Sensor 2 signal.

The 3X is called the sync pulse. Each sync pulse represents a pair of companion cylinders and is also used by the ICM for a fast start. The 18X reference pulses are passed from the CKP sensor to the ICM on the CKP sensor 1 signal circuit. The ICM uses the CKP Sensor 1 18X and CKP Sensor 2 3X sync pulses to determine the crankshaft position by counting how many ON-OFF 18X pulses occur during a sync pulse. With this dual interrupter ring arrangement the ICM can identify the correct pair of cylinders to fire within as little as 120 degrees of crankshaft rotation for a fast start.

The ICM uses the CKP Sensor 1 and 2 signals to determine the correct coil triggering sequence, based on how many 18X ON-OFF pulses occur during a sync pulse. The ICM will also determine the correct direction of the crankshaft rotation, and will prevent spark to the coils to prevent damage from backfiring if reverse rotation is detected. Coil sequencing occurs at start-up, and is remembered by the ICM. Once the engine is running, the ICM will continue to trigger the coils without the CKP sync pulse.

The 18X CKP Sensor 1 signal is used by the ICM to convert the analog signal to a digital 3X signal for use by the PCM. The ICM divides the 18X signal pulses by 6. This divider circuit will not begin operation without a sync pulse present at start-up.

The 18X CKP Sensor 1 signal is also used by the ICM to convert the analog signal to a digital 18X signal for use by the PCM.