Ignition Control Module (ICM)

Ignition Control Module (ICM)

The ignition control (IC) spark timing is the PCM's method of controlling the spark advance and the ignition dwell.
The IC spark advance and the ignition dwell are calculated by the PCM using the following inputs:
- Engine speed.
- Crankshaft position (58X reference).
- Camshaft position (CMP) sensor.
- Engine coolant temperature (ECT) sensor.
- Throttle position (TP) sensor.
- Knock signal (knock sensor).
- Park/Neutral position (PRNDL input).
- Vehicle speed (vehicle speed sensor). PCM and ignition system supply voltage.





- The crankshaft positron (CKP) sensor sends the PCM a 58X signal related to the exact position of the crankshaft.
- The camshaft position (CMP) sensor sends a signal related to the position of the camshaft.




- The knock sensor tells the PCM if there is any problem with pre-ignition or detonation. This information allows the PCM to retard timing, if necessary.




Based on these sensor signals and engine load information, the PCM sends 5V to each ignition coil.




The PCM applies 5V signal voltage to the ignition coil requiring ignition. This signal sets on the power transistor of the ignition coil to establish a grounding circuit for the primary coil, applying battery voltage to the primary coil. At the ignition timing, the PCM stops sending the 5V signal voltage. Under this condition the power transistor of the ignition coil is set oft to cut the battery voltage to the primary coil, thereby causing a magnetic field generated in the primary coil to collapse. On this moment a line of magnetic force flows to the secondary coil, and when this magnetic line crosses the coil, high voltage induced by the secondary ignition circuit to flow through the spark plug to the ground.