ECU stands for engine control unit and it is the computer that serves as kind of the brain for your car's engine. Also known as an ECM or engine control module, these computers run most of the systems and subsystems that keep your engine functioning.
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Even though you can trace the development of this technology back decades, they didn't really become prominent features and vehicles until the 80s. And of course, as computer technology progressed, they became much more advanced in the modern age. They are essential for the function of any motor vehicle and nearly every system in your car will in some way rely on the ECU. That's not to say everything requires ECU to function, but it is a large part of the overall car's ability to perform.
Because the ECU controls so much of how your engine operates, if your ECU fails then you can expect some serious problems with how your car functions.
How Does an Engine Control Unit Work?
Your engine control unit is a computer system that operates by way of a network of sensors. These sensors monitor fuel economy as well as emissions, fuel injection and many other aspects of how your engine functions. For instance, through the use of a crankshaft position sensor it’s able to accurately gauge the position of the pistons in your engine so that fuel and oxygen are added at the right time. It then ensures spark goes off at the right time. The ECU is integral for all of these sensors to be precisely aligned so that the ECU can function properly.
If the ECU on your car is also responsible for the operation of the powertrain then it’s called a Powertrain Control Module or PCM.
When your engine control unit is working properly it is able to ensure that any function of your engine is operating the way it's supposed to be. When something goes wrong, this is the system that will set off a check engine light that corresponds to the problem. When you go to a mechanic to help you diagnose any problems with your car, they'll use an onboard diagnostic tool that hooks into the ECU to get a more clear picture of what's malfunctioning in the car. You can consider it something like the nervous system of your entire vehicle.
Signs That Your Engine Control Unit is Malfunctioning
A malfunctioning ECU can cause a host of difficulties with your car. Some of them can be mild nuisances whereas if a problem is bad enough you could render your car entirely undrivable. It's always best to find out the nature of the problem when your ECU is malfunctioning to ensure that you're able to continue using your car.
There are a handful of things you should be on the lookout for to help you figure out if your car's engine control unit is malfunctioning.
- Check Engine Light is On. Many problems can cause the check engine light to come on, but a faulty ECU will almost always trip this warning light. Unfortunately, because there are so many potential reasons for the check engine light coming on, once it pops up you're going to need to have a mechanic diagnose the issue fully to find out if it is in fact your ECU that's the problem.
If your check engine light is on and stays on no matter what you do, that's a good sign that your engine control unit is malfunctioning. If it were another issue it's more likely that the light would have turn off at some point.
- Poor Fuel Economy. If you find your car struggling for no reason that is readily apparent, and your fuel economy drops noticeably it's possible that you are ECU is no longer able to maintain your fuel system properly and the result is a drop and efficiency.
- Engine Misfires. The engine control unit is responsible for maintaining your engine's timing. If it starts to be a function, the timing can potentially go off in your engine will be firing at the wrong moment. That causes an extreme dip in performance as well as noises that are hard to miss.
One of the functions of your engine control unit is spark timing. The way your engine sparks and fires the fuel / oxygen mixture is are usually the most precisely timed system in your entire car. If this becomes misaligned, then you can expect serious and potentially destructive engine misfires.
- Engine Stalling. If you find the engine stalling on you intermittently, either as you're trying to start the car or even when you idle at red lights, that's a potential sign of a faulty ECU.
- Your Car Won't Start. If the car simply will not start at all it's possible that your ECU has failed on you. If the ECU doesn't function at all then your engine management is completely offline, and the car will no longer function for you.
- Flooded Engine. On rare occasions if you find your car nearly submerged in water, typically this happens if you try to cross a flooded road, you may find the entire thing stalls out because your engine flooded. If this happened, then it spells bad news for your ECM. If your engine control unit has been flooded out by water, it's likely completely dead at this point and will need to be replaced. This is a rare problem, but it's not something everyone thinks of when their engine sustains some serious water damage.
If you experience any of these problems, it's best to head to a mechanic to have the issue diagnosed. You absolutely cannot drive a car with a faulty ECU. While it may be functional for a while the potential for catastrophic failure does exist. If the ECU fails completely then your car is not drivable.
The Cost of Fixing a Bad Engine Control Unit
A malfunctioning engine control unit is a potentially costly repair compared to many other repairs that you may have to get done on your car. Obviously, the cost of repairs is very much dependent on a number of factors. Your ECU repair cost is affected by:
- The make, model, and year of your vehicle
- The state you live in
- The mechanic you choose
- The repair method you opt for
No doubt you've noticed in the other car repairs that a mechanic on one side of town can charge an entirely different amount for the same repair compared to another mechanic on the other side of town. As with any repairs, it's best to call around and get estimates ahead of time.
In general, the cost of replacing your engine control unit is going to be anywhere from $1,000 to $3,000. That's the cost of the entire ECU if you're buying it brand new, however. You need to be aware that replacing the ECU entirely is not always necessary. In fact, in many cases it can be reprogrammed which can save you a lot of money. If you don't need a new part, it's best to fix the old ECU to get it back to a functional standard.
To get an ECU diagnostic from a mechanic it's probably going to cost you somewhere around $100 to $300. That will get you to the point where you know for sure what is wrong with it, and your mechanic should be able to determine how they will fix it at that point.
If you just need a reprogramming for your ECU as opposed to a complete repair, you're looking at a price range of about $300 to $800. As you can see, that's quite a range. Unfortunately, it really does depend heavily on the make and model of your vehicle. More exotic vehicles are likely to cost you more in the long run when it comes to repairing or replacing an engine control unit.
Online Repair
There is another option for repairing your engine control unit that may work for you. There are a number of businesses that operate online these days repairing engine control units. They require you to physically send the hardware into them and they'll be able to turn it around in a few days and send the repaired unit back to you in the mail.
The trade-off for the extra time involved here is that it's often much cheaper than taking it to your mechanic. In some cases, you can potentially cut the bill in half if you're willing to wait a few days to get it back. Of course, you have to be comfortable removing the part yourself, or taking it to a mechanic who can take it out for you at and you'll have to add that cost on top.
Always read the online review of a business like this before committing to anything. Make sure the business is trustworthy.
Repair Auctions
There is a second version of online repairs that you may take advantage of if you're so inclined. If you head to eBay, you can actually search for your make and model engine control unit. It's very likely that you'll get a result from a company offering a repair and return service. You bid on the auction, you said in your part, they repair it and send it back to you. This is even cheaper than me online repair services in many cases. You can potentially get your engine control unit repaired for under $100 this way. Some makes and models have auctions that will start under $50.
If you opt for getting an auction repair service, you definitely have to make sure you're checking their feedback first. Just like you want to check the reputation of any local mechanic, you need to be extra careful when dealing with someone online. Since you can't physically go see the shop or get a feel for who's doing the repairs. You have to rely on their feedback ratings. Fortunately, eBay is pretty reliable this way. So long as the company has a good number of reviews that are positive, you're probably safe to go ahead with bidding on the auction. Use your best judgement though.
The other thing to keep in mind with an online auction is there is also an added cost for shipping that you need to be aware of. Sometimes shipping costs can be higher than you expect oh, so factor that into the overall price. In many cases it's still much more cost-effective then Heading to a local mechanic.
Timing with an eBay auction is probably your biggest concern. Make sure that the auction clearly states how long it will take to get your heart back to you. And you also need to be aware of how quickly you can get it to them in the first place.
Can I Repair the ECU Myself?
There are two ways to approach a DIY ECU repair. Replacing it yourself is actually easier than repairing it yourself, but you will need a new piece of hardware that is preprogrammed to work with your exact make and model. If you have the confidence to give it a try you can find videos online that explain the process. You need to make sure you’re ordering the right part and that it’s an OEM part guaranteed to work with your vehicle.
Repairing rather than replacing the ECU requires a fair bit of tech know-how. If you’re not skilled in managing this kind of technology, then it’s best to leave this to a professional. You never want to risk a component as important as your ECU if you're not fully confident on how to repair it.
If you want to make sure your car is running at optimum then your best bet is to take it to a professional mechanic whenever you notice a problem so that they can both diagnose and repair the issue for you. Only consider doing it yourself if you know what you’re doing and have practice getting the job done already. It will save you more money in the long run.