Can You Reprogram A Used ECU?

The Electronic Control Unit (ECU, aka Engine Control Module or ECM) manages just about every aspect of your engine. You are most likely reading this because your ECU is either faulty or has failed completely. And as you might have already found out, a broken ECU can leave you stranded by the roadside.

What you may not know is that every car has a unique ECU. So, the next question is can you reprogram another ECU to work with your car? The short answer is yes. But there are some important things to know before buying a replacement part.

Why Would You Reprogram An ECU?

Every modern car on the road today has an ECU that controls and monitors its engine. It optimizes the fuel/air ratio to maximize efficiency. Read our blog on ‘What Is An ECM/ECU And Why Is It Important?’ to find out more on this topic.

If the ECU fails you will need a replacement unit, otherwise the car will be going nowhere. ECUs are programmed to work in the car they are fitted to. They have unique coding for the vehicle’s immobilizer, too.

That’s why just swapping out your old ECU with an apparently identical one from the same make and model won’t work. It will have to be reprogrammed first. It will then be able to communicate with your car key and immobilizer.

How Do You Reprogram An ECU?

Remove ECUImage Credit: AutoRepairGuys

Physically removing and replacing your ECU is not a difficult job. And if you need to reprogram it, you have three options.

  • Dealer Reprogramming: Before you buy the replacement ECU, contact your nearest dealer to see if they will reprogram it for you. Most are more than happy to oblige, although some may be unwilling to help out if you didn’t buy the ECU from them.
  • Specialist Reprogramming: If the dealer can’t or won’t help you, there are plenty of specialists around that are happy to do it. Some mechanics also have the required ECU reprogramming tools.
  • DIY Reprogramming: Every car sold since 1996 will have what is called an OBDII port. This has a connector – usually just below the dash on the driver’s side – into which you can plug a diagnostic device. There are several OBD II reprogramming tools available online. Some only allow for code checking and clearing. Others also let you reprogram the ECU. These tend to be the pricier options, so they may end up costing more than the labor a dealer would charge for the same job. Cars built between 1991 and 1996 came fitted with an OBD I port, while pre-1991 cars don’t have one at all. The good news is that many of these older models do not have factory immobilizer systems. So, they might not require an ECU reprogram.

Which Car Makes Need ECU/ECM Reprogramming?

There is no definitive list of vehicles that need ECU reprogramming. Although, most newer vehicles and certainly ones with immobilizers will need to have it done.

While your best bet is to contact your dealer, we have found that newer models from the following makes almost always need an ECU reprogram:

The majority of these vehicles come with a factory immobilizer. This will need to be matched to the replacement ECU.

Buying A Replacement ECU

Replace ecu

At Tom’s Foreign Auto Parts we stock thousands of quality used ECUs. To ensure that you find the right replacement the first time, get in touch with our team and provide us with your old ECU part number.

Supplying us with the new part number from your dealer won’t work, as this may differ from what we have on our systems.

ECU Reprogramming Checklist

Reprogramming your ECU/ECM yourself is doable – follow this checklist to be sure you’re getting the job done right:

  • Contact your dealer to see if a replacement ECU will need programming.
  • Get in touch with Tom’s Foreign Auto Parts with your old ECU part number.
  • Order a quality used OEM ECU – with our 6-month guarantee.
  • Purchase an OBDII ECU reprogramming tool – or confirm with your dealer or mechanic that they will reprogram the replacement ECU for you.
  • Once you have received the replacement part and it has been reprogrammed, you are all set.

We only sell quality used OEM parts. And we offer a 6-month no hassle money back guarantee to back them up. There really is no reason to buy new when you can save up to 75% with perfectly good used OEM parts from Tom’s Foreign Auto Parts.