How to Replace a GM Ignition Module

GM family engine close up.

Rinor_Kryeziu/Wikimedia Commons/CC BY 3.0

In a GM car or truck with a V8 engine, the ignition control module (also known as the ICM) is hiding under the distributor cap. Chevy trucks, GMC trucks, or any General Motors vehicle with this type of eight-cylinder engine will be the same. If you drive a different vehicle, the process will be very similar.

of 05

The GM Ignition Module

Junkyard with multiple cars and three old Chevy models in a late fall landscape.

Richard/Flickr/CC BY 2.0

First, get a new ignition control module for your vehicle. These can be found both in physical stores and junkyards. Ignition control modules can also be purchased online.

of 05

Access the ICM

Close up of an engine air filter in chrome.

Sherman Ray/Pexels

The first thing that needs to be removed to access the distributor is the air cleaner assembly. To remove this, there are a couple of connections that need to come off first. There is a breather hose attached underneath toward the front of the engine compartment. This pulls off easily. Next, remove the larger preheat tube from the bottom of the air cleaner. This should also pull right off, although it might be a little stuck from being on there so long. Remove the wing nut from the top of the air cleaner and take off the cover. With the air cleaner element removed, you may see a couple of small bolts attaching the air cleaner assembly. If you're not sure, give it a firm tug upward and, if it doesn't pop off or at least shift a lot, you need to remove some bolts first.

of 05

Removing the Ignition Control Module

Distributor cap and spark plugs in a classic car close up.

MWCPhoto/Getty Images

With the air filter assembly removed, you can see the spark plug wires and distributor cap. You will need to remove the distributor cap to access the ignition control module, but do not remove all of those plug wires! It's not a necessary step and there's always a real chance that you'll screw up the firing order when you reinstall them and have to go back to square one. Leaving them attached to the distributor cap is a much easier move. Remove the two bolts that attach the cap to the distributor and move the cap to the side. You'll see a black plastic piece. This is the module you're looking for. Remove the two electrical plugs on the side, then remove the two screws that are attaching the ICM to the distributor. 

of 05

Applying the Dielectric Grease

Gloved hands using silicone past, also known as dielectric grease, on a car engine.

Photo from Amazon

You're now ready to install the new ignition control module. It's nice and clean, but we need to dirty it up a bit with the dielectric grease. This grease is essential for creating a positive and lasting connection between the ICM and the information it needs from the distributor. The grease was included with your replacement ignition module. Apply a liberal coat before you start the process of installing the module. 

of 05

Reinstallation of Parts

Engine with air filter and all hoses attached.


Attach the two screws to your new ICM and reinstall the wiring harnesses. Next, reinstall your distributor cap. Aren't you glad you don't have to put all of those plug wires back now? Attach the two screws holding the cap in place. Now put the air cleaner assembly back on (if yours had screws or bolts, put them back, too). Attach the cover of the air filter assembly and tighten the wing nut. Don't forget to replace the two hoses you removed from underneath the assembly. You're done!