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.
- Vehicle speed (vehicle speed sensor).
- PCM and ignition system supply voltage.




The powertrain control module (PCM) controls engine ignition through a solid-state switching unit called the ignition control module (1CM). The software in the PCM uses input from several sensors to determine the timing, duration, and strength of the spark.




- The crankshaft position (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.

Based on these sensor signals, as well as engine load and engine coolant temperature information, the PCM controls the switching function of the ICM by sending it a 5V signal. As long as the ICM receives the signal, it allows battery voltage to the ignition coil. That voltage allows a magnetic field to build in the coil.

When the PCM requires a spark plug to fire, it shuts off the 5V signal to the ICM grounding it internally. This triggers the ICM to switch off the battery voltage to the ignition coil, which causes the field to collapse. The lines of magnetic force pass through the secondary portion of the coil as they collapse. As they intersect the coil, they induce high voltage in the secondary ignition circuit which travels toward ground through the spark plug.