What Is the Ignition Control Module on a Car?

by Andrea SteinUpdated July 07, 2023
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Classic Car Engine Refurbished image by Janet Wall from Fotolia.com

An ignition coil is the coil in a vehicle's ignition system used to convert sufficient voltage to spark the spark plugs. The ignition control module helps manage the electrical current used by the ignition coil. This helps manage engine misfires, stalling, and other common symptoms of engine performance like coolant emissions, no spark, overheating, and fuel mixture issues. It connects to the check engine light and can help with diagnosing of electronic ignition problems.


The ignition control module (ICM) typically mounts on the engine. Some components in ignition control modules are heat-sensitive, thus modules are often covered in insulating material around the internal circuitry.

A heat shield may also be placed between the engine and ignition control module to protect against the high voltage ignition switch, especially during auto repair of the catalytic converter or coil packs near hot contact points.


The ignition control module switches transistors on and off based on input from the magnetic pulse generator in the distributor of the control unit. The magnetic pulse generators transmits an AC voltage signal that corresponds with engine speed and the position of the crankshaft position.

The ignition control module converts the analog signal into a digital signal, which essentially is used as an on/off switch by the ignition control module. There are different sensors that send signals to the powertrain control module, including the camshaft position sensor and the crankshaft position sensor.

Ignition Timing

When an engine starts, the ignition system operates via module timing of the wiring harness. The engine control module signals the ignition control module, which trips a switch in the ignition control module multimeter. Activating this switch enables the primary circuit transistor to operate via signals from the engine control module.

The engine control module (ECM) can then calculate ignition timing based on engine information sensors, such as engine speed and engine load. When these things aren’t functioning properly, then the test light will come on, as long as your car is in warranty, and you know you need to take it into the repair shop to fix a bad ignition control module.

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