Every modern vehicle has an Engine Control Unit (ECU). Its job is to coordinate and manage the engine’s various complex systems. A faulty ECU can cause rough running and poor gas mileage and will eventually prevent your car from working at all.

This ECU buyer’s guide will cover everything you need to know. From common issues to diagnosis and replacement we have it all here. We’ll cover topics like:

• What are ECMs/ECUs, and what do they do?
• Can an ECU be reprogrammed?
• Common ECU issues/problems
• How to diagnose a failing ECU
• OEM vs. Aftermarket ECM options – which is better?
• How to replace your ECM/ECU

What Is An ECU And Why Is It Important?

Whether you call it an Engine Control Module (ECM) or an Engine Control Unit (ECU), it refers to the same thing. It is an onboard computer that controls how your engine works.

A modern engine has many complex components that must work together to achieve the best efficiency and driveability possible. The ECU manages this by checking the performance of every component many times a second. Then, it makes adjustments as required. For more information on the subject, read about it in our ‘What Is An ECM And Why Is It Important’ article.

Can You Reprogram A Used ECU?

The short answer is yes. Almost every modern car will need its replacement ECU to be reprogrammed before it works correctly. Reprogramming can be done by the dealer, a specialist, or you if you have the required reprogramming tools.

Older cars (think pre-1991) may work without needing an ECU reprogram, but always check with the dealer first. Read our comprehensive post on the subject here.

Common ECU Problems

Your car’s ECU controls so many aspects of the engine that it can cause several issues when it starts playing up.

Faulty ECU Symptoms:

• The car does not idle well or stalls for no apparent reason
• Jerking and hesitation when accelerating
• Engine warning light on the dashboard
• The key won’t lock or unlock the vehicle

Faulty ECU Issues:

• Damaged or corroded wires
• Engine sensor issues
• Water or power surge damage to the ECU box

Read our Common ECM/ECU Problems blog to learn more on this subject.

How To Diagnose A Failing ECU

If you are experiencing the symptoms and issues above, it’s a good idea to confirm the source of the problem before replacing the ECU. The first step is to use an OBDII scanner to see whether fault codes appear. Most vehicles built on or after 1994/95 should have an OBDII port. You should also check the ECU for physical damage. Burn marks, water damage, or bent/broken wiring are all surefire signs that the ECU is at fault.

To learn more about diagnosing your ECU, check out this article.

OEM Vs. Aftermarket Engine Control Modules

If you have identified the ECU as the source of your car troubles, it’s time to get a replacement. You may be considering an aftermarket option to save some money. But you may end up damaging your car’s sensitive electrical components, which could cost you even more.

OEM ECUs will work perfectly, and ensure that your vehicle operates exactly as the manufacturer intended. They are also covered by the manufacturer’s guarantee.

But OEM ECUs can be expensive. That’s why opting for one of our quality used OEM ECUs is the best way to go. You can save up to 75% off new prices, and you still benefit from our industry-leading guarantee.

Check out this blog post to learn more about why OEM parts are the superior choice.

How To Replace An Engine Control Module

Now that you have received your quality used OEM ECU from Tom’s, it’s time to replace it. Make sure you have had the replacement ECU reprogrammed beforehand.

Replacing an ECU by yourself is a great way to save money on labor charges. The tools required should already be in most auto enthusiasts’ toolboxes already. The process is relatively simple and similar across many makes and models. We cover a detailed ECM replacement procedure for Honda and Infiniti models in our tutorial here.

Replacement ECUs From Tom’s Foreign Auto Parts

Diagnosing, buying, and replacing an ECU can be time-consuming and expensive. But once you’ve gone through our comprehensive ECU buyer’s guide, you’ll see that it can be done for far less money and hassle than you might think.

Buying a quality used ECU from Tom’s can save you up to 75% off new prices. Diagnosing and installing it yourself will save on labor charges, too. We offer a no-hassle 6-month money-back guarantee for extra peace of mind.

We stock thousands of ECM modules for many popular brands, including Honda, Infiniti and Toyota. Contact us online and get your quality used OEM replacement ECU today.