Ignition Control Module (ICM) and Ignition Coils

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 18 X 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 input.
^ The ICM inputs 18 X and 3 X reference signals to the PCM.
^ The 3 X 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 18 X signal pulses by six. This divider circuit will not begin operation without a sync pulse present at start-up, and without 18 X and 3 X reference signals no fuel injection will occur.