How To Diagnose A Failing Engine Control Module/Electronic Control Unit

A failed ECU will stop your car from working. If you suspect your Electronic Control Module (ECU) – also known as the ECM (Engine Control Module) – is failing, there are several ways to diagnose it before that happens.

Avoid getting stuck by the side of the road by learning how to diagnose and troubleshoot a failing ECU.

What Are The Signs Of A Failing ECU?

check engine light

Your vehicle’s ECU ensures that many complex engine systems work in harmony (learn more about the ECU’s job here). If it starts to give problems, many of these components won’t work properly. If you start experiencing the following issues, the ECU may be at fault:

  • Engine stalls randomly
  • Loss of power
  • Fuel economy suddenly gets worse
  • Engine warning light goes on
  • Engine won’t start
  • Vehicle key stops responding

These symptoms can also occur from other issues. So, troubleshooting is required to ensure that the ECU is the root of your problems. Read our informative blog here for a more in-depth look into common ECU problems.

When Should You Test The ECU?

ECM pins

Replacing your ECU without first testing it can be an expensive mistake. A stalling engine and poor fuel economy could also be from fuel system issues. An engine warning light can illuminate for dozens of reasons. But if you are experiencing several of the issues above, it’s time to test the ECU module.

ECU Testing Methods

Your vehicle’s ECU is usually in the footwell or under the hood. Check your owner’s manual to find its exact location. You will need a few tools to complete this process:

  • Screwdriver set
  • Sharp blade or box cutter
  • Pliers
  • Flashlight
  • OBDII Scanner

1. Use An OBDII Scanner To Test Your Electronic Control Unit

Most vehicles since around 1994/95 have an OBD2 port. An OBD2 scanner can be plugged into this port to check for engine fault codes. If you have access to an OBD2 scanner, it can quickly reveal whether your ECU is failing.

Depending on the type of OBD2 scanner you have, you can change engine parameters, run an emissions test and read diagnostic trouble codes. This last one is the most important when testing an ECU. If you are unfamiliar with Diagnostic Trouble Codes (DTC) then look the error code up online. The letter P before a set of numbers indicates an issue with the powertrain.

2. Physically Check The Engine Control Module

This may seem rather obvious, but physical damage may not be apparent until you take a closer look at the module. Use a flashlight to check for signs of damage around the ECU. Remove the wiring harness and make sure the wires aren’t broken, corroded, burnt, or bent. Examine throughly for burn marks, water damage and loose, weak or bent pins.

Most ECU modules are sealed units. Some can be opened by removing any retaining screws and carefully pulling away the cover using a flat head screwdriver or sharp knife. Carefully examine the PC board for any signs of water or heat damage. Remove the negative battery terminal before handling the ECU.

Replace Your Failing ECM With A Quality Used OEM Part

If your ECU shows signs of physical damage, or the OBDII scanner has thrown up an error code it’s time for a replacement unit. Tom’s Foreign Auto Parts stocks thousands of quality used OEM ECUs with an industry-leading guarantee. You can save up to 75% off new ECU prices for Acura, Honda, Infiniti, and many other brands.

We have been providing quality used OEM parts for over 30 years. Get in touch online or browse our broad range of quality used OEM ECUs here.