Ignition Control Module: Description and Operation
DESCRIPTION AND OPERATIONThe powertrain control module (PCM) controls engine ignition through a solid-state switching unit called the ignition control module (ICM). The software in the PCM uses input from several sensors to determine the timing, duration, and strength of the spark.
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 coils.
When the PCM (1) requires each spark plug to fire, it shuts off the 5V (2) signal to the ICM (3) for that plug by grounding it internally. This triggers the transistors in the ICM to switch off the battery voltage to the ignition coil (4), 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.