Rick's Free Auto Repair Advice

ECM Repair

How to perform an ECM Repair

The engine control module (ECM) is the main computer in your vehicle. Each carmaker refers to it by a different name. Some call it a powertrain control module (PCM). Others call it an engine control unit (ECU). A PCM controls both the engine and the transmission, while an ECM or ECU usually only controls the engine. In vehicles with an ECU or ECM, there’s usually another module to control the transmission.

When to do an ECM repair or replace an ECM?

Many DIYers jump to the conclusion that the ECM is the cause of their problems. In reality, ECMs, PCMs, and ECUs rarely fail. When they do, it’s often caused by another component, like a failed ignition coil.

If you’ve performed all the diagnostic testing and confirmed beyond a doubt that the problem is the ECM, then you have only three choices: 1) buy a new unit from the dealer, 2) get yours rebuild from a competent module rebuilder, or 3) find one and a junkyard.

ECM repair

Image by Moduleexperts.com

The new dealer unit will cost the most and you’ll have to pay to have it programmed to your specific VIN. But it will be the most readily available.

Getting yours rebuilt is usually the best option since the rebuilder knows the most common failure points and can upgrade the unit to prevent future failures. Just make sure the rebuilder you choose also programs the unit to your VIN so it’s plug-and-play once you get it.

The junkyard version is the least attractive option since you really don’t know it’s condition and you still have to pay to have it programmed to your VIN.

How to get your ECM rebuilt

Several online companies offer rebuilding services. Find one with good online reviews. Then remove yours, Warp it in tin foil to prevent static discharge during transit and overnight it to the rebuilder.

How to replace an ECM

Disconnect the battery terminals from your battery. Let the vehicle sit for about five minutes to allow the airbag system to de-power.

Locate the ECM and disconnect each of the connectors, noting their location on the ECM. Then remove any hold-down brackets and remove the ECM.

When you receive the new, used, or rebuilt unit, reverse the installation, making sure that the battery is disconnected the entire time.

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Posted on by Rick Muscoplat

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