Ignition Control Module: Description and Operation

Three dual tower ignition coils are mounted to the ICM, and are serviced individually. The ICM performs the following functions:
- The ICM supplies a power and low reference circuit to the CMP and CKP sensors.
- The ICM determines the correct direction of the crankshaft rotation, and cuts spark and fuel delivery to prevent damage from backfiring if reverse rotation is detected.
- The ICM determines the correct coil triggering sequence, based on how many 18X ON-OFF pulses occur during a sync pulse. This coil sequencing occurs at start-up, and is remembered by the ICM. After the engine is running, the ICM will continue to trigger the coils without the CKP sync pulse.
- The ICM inputs 18X and 3X reference signals to the PCM.
- The 3X reference signal is also known as the low resolution engine speed signal. This signal is generated by the ICM using an internal divide-by-six circuit. This circuit divides the 18X signal pulses by 6. This divider circuit will not begin operation without a sync pulse present at start-up, and without 18X and 3X reference signals no fuel injection will occur.