Bad ECU Symptoms and Replacement Cost

The engine control unit, or ECU, of a vehicle is an electronic module that controls the function of the engine. This is done through a series of electronic components and sensors which compute data back to the engine. Based on what this data indicates, the engine will perform a specific function. If your vehicle has a bad engine control unit, then it can cause all kinds of problems with how the engine functions. As a result, it will impair your ability to operate your vehicle safely and effectively on the road.

Bad ECU Symptoms

Fortunately, there are certain symptoms that you can look out for early on to detect if your engine control unit is going bad. The easiest symptom to recognize is when the “Check Engine” warning light illuminates on the dashboard. Of course, there are many possible reasons for why this warning light would illuminate. But in cases where the engine control unit detects issues with its electronic components, circuits, and/or sensors, it will immediately cause the Check Engine warning light to illuminate. Sometimes the engine control unit will do this by mistake too. To figure out if the engine control unit is truly having problems, you need to search for the specific trouble codes on your vehicle’s computer. These codes will identify the root of the problem. Check with your manufacturer or owner’s manual to learn more about trouble codes.

Another symptom that may follow a warning light illumination is an engine that misfires or maybe even stalls. There won’t really be any consistency with these issues either. The pattern of engine misfires and stalls will be random, making it hard to pinpoint the specific engine problem. Often times, this is because the engine control unit is failing and it’s feeding the engine some false information. If the problem gets worse, the performance of the engine will deteriorate while it’s running. You may experience weak acceleration, low power, and reduced fuel economy and efficiency.

The worst symptom is when your car does not start at all. It may be difficult to start at first but then, it will never start up again. This happens after the engine control unit goes completely bad and does not function at all. Once that happens, the engine has no computer system to control and guide its own functionality. Although you may still be able to crank the engine, it will not start because the computer is not feeding it the important information it needs to perform its job. Again, there could be other reasons for your engine not starting up too. The only true way to know if this symptom is related to a failing engine control unit is to have it inspected by a certified auto technician.

The ECU Replacement Cost

If it is discovered that you truly do have a bad engine control unit, then you will have no choice but to purchase a replacement unit. The cost of an engine control unit replacement will depend on the make and model of your vehicle. On average, you can expect the parts cost to be anywhere from $500 to $2,500 while the labor costs are roughly from $100 to $200. The average owner of an economy car will end up spending close to $1,000 for a replacement job. In some circumstances, an existing warranty on the vehicle may cover this expense if the engine control unit fails prematurely.

Read also: Does cruise control save gas? 10 Benefits of using Cruise control

Sometimes you may have a problem with the engine control unit that can simply be repaired. This will certainly save you the huge expense of having to pay for an entirely new unit. However, in most cases, the unit will have to be replaced. The only real time when a repair job will be necessary is if there’s merely a configuration problem with the computer.



  1. My ECU is not working well. A.C does not function. Garage stated they called Germany and Mercedez said, “Vell we’re sorry we don’t make that ECM anymore.” Vehicle is a 2002 500sl. Any idea what’s the best avenue? Please let me know.

    • There should be plenty of ECUs for a 2002 MB available. Your local dealership should be able to get a new one ($$$) but many companies sell remanufactured ones, eBay sells used ones, and many wrecking yards (some are MB specific) should be able to sell you one. You will likely need to also have it reprogrammed for your vehicle but again, many online companies offer this service as well.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.