Ignition Control Module

The 3X reference signal is produced by the Ignition Control Module (ICM). The ICM calculates the 3X reference signal by dividing the Crankshaft Position (CKP) sensor 18X pulses by 3 when the engine is running and CKP sync pulses are also being received. The Powertrain Control Module (PCM) uses the 3X reference signal to calculate engine RPM and crankshaft position at engine speeds above 1200 RPM. The PCM also uses the pulses on this circuit to initiate injector pulses. The PCM constantly monitors the number of pulses on the 3X reference circuit and compares the number of 3X reference pulses to the number of 18X reference pulses and CAM signal pulses being received. The PCM will use the 18X reference signal circuit for fuel and ignition control. The engine will continue to start and run using the 18X reference and camshaft position PCM input signals only. If the PCM detects an incorrect number of pulses on the 3X reference circuit, DTC P1374 sets.

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.