Last Updated on August 5, 2022
The engine control unit (ECU), also referred to as the engine control module (ECM), 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.
Related: Symptoms of a Bad Powertrain Control Module (PCM)
Top 5 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.
#1 – Check Engine Light
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, owner’s manual, our site, or various online resources to learn more about trouble codes.
Related: P0606 Code, P2509 Code, U0073 Code, U0100 Code, U1000 Code
#2 – Engine Misfires or Stalls
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 module 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.
#3 – Bad Gas Mileage
Since a proper air-fuel ratio is needed for a vehicle to function optimally, a bad ECM won’t understand how much fuel should be sent to the combustion chamber. This means too much fuel is often sent to burn in the combustion process.
The result is that your vehicle will then be running rich and using more fuel than necessary. Not only will you have to budget more for gasoline each month, you won’t be doing the atmosphere any favors.
#4 – Poor Engine Performance
Alternatively, a faulty ECM may also cause not enough fuel to be delivered to the combustion chamber. This means that when you step on the gas, your car simply won’t accelerate like it used to.
It may even shake and vibrate some, especially when trying to go up hills, when there’s a lot of extra weight in the car, or when you’re towing something. You may also experience a rough idle due to not having enough fuel for the conditions.
#5 – Car Won’t Start
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 has a complete failure 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.
ECU Replacement Cost
If it is discovered that you truly do have a bad engine control module, then you will have no choice but to purchase a replacement unit or possibly repair it. The cost of an engine control unit replacement will depend heavily on the make and model of your vehicle.
The more complex and technologically advanced a vehicle is, the more you will likely pay. ECUs for luxury vehicle brands will cost much more than that of a typical economy car. It’s similar to buying a top of the line MacBook Pro from Apple versus a budget computer from Walmart.
On average, you can expect the parts cost to be anywhere from $400 to $1,400 while the labor costs are roughly from $100 to $200 for reprogramming and installation. You may be able to save some money on a refurbished ECU but that usually comes with a bit of risk.
Related: BCM Replacement Cost
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.
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.
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38 thoughts on “5 Symptoms of a Bad ECU (and Replacement Cost)”
An exact match, used, is a great start and the best way to save time, money and aggravation. Make sure you get one that you can return without penalty. ie restocking fee.
What is the price of an ECU for mercedes year 2009 E230 W212, Mercedes quote MR 19000.
I was 1 hour into a road trip in my 2009 Subaru Outback when the engine suddenly shut off and I had to cost to the side of the road and eventually get it towed back home. It turns over but will not start. Mine code reader gives me two codes, a P0600 and P0340 with a ER HC on the odometer. I have replaced the camshaft position sensor with no change. There was no check engine light on or any warning prior to the engine shutting off.
Sounds like this may be a wiring or grounding issue. I would start at the cam sensor wiring and work your way towards the main engine harness connector, that connects the rest of the wiring harness to the connectors attached to the intake manifold. Inspect the wiring to make sure there is no visible damage to the insulation. Check that all grounds are tight and free of corrosion.
If you do have an electrical issue like this, you may be able to replicate the issue by jiggling the wiring around in different places while the car is running. Be careful to keep your hands away from hot and moving components if you decide to try this yourself.
Check engine light went one on Honda Accord 2004 EX.
ODB link returns error code P0325 Knock Sensor 1 Circuit. No other error codes, I have not driven the car much since it happened a few days ago (~ 16 miles) but the ride does not feel any different, the car does not vibrate or shake, even when going up moderate hills and I do not feel a loss of power, but again, it have driven the car less than 20 miles.
The ECM and related sensors were never repaired or replaced, they are the original ones and the car has ~92,000 miles on it.
Is this just a Knock Sensor gone bad?
Should I see other error codes returned by diagnostics if the ECM unit went bad?
Could be a bad knock sensor. It’s probably not a bad ECM. You could look up a factory service manual to test the knock sensor, or try just replacing the sensor if that’s easier. The factory manual should have a wiring diagram for that system, and also a process that you can use to test the knock sensor using a multimeter. I like to test components before I replace them so I don’t waste money replacing the wrong parts.
I have a 2009 GMC sierra and no CH MSL does not work at all the brake lights do work and the cargo lights work what could this be the fuses are good
I own a VW Vento 1.6TDI 2011 make.Now the engine speed is restricting to 1600 rpm. So I cannot drive the vehicle above 55-60 km speed and finding it difficult to overtake. The vehicle is running smoothly in these speed limits.The coil light and engine light is glowing. The VW service centre scanned the vehicle and told that ECM is faulty and needs replacement. All other modules and sensors are working perfectly. Other car mechanics also scanned and told that ECM is faulty. The probable cause is a software error. But the VW is not ready to re program it and said they don’t have such a work in their service schedule since the vehicle is Ten years old. The Error code is 0606. The vehicle is running at this condition for the last one month. Can anyone help me.
If the consensus is a failed ECM you could try finding a replacement at a salvage yard and swapping it in. I would look on forums to learn how to do this, and see if any additional steps are required to program the new ECM.
How much is it to recode a Nissan narvardo 2012 truck and who can do the recoding
My Nissan narvardo 2013 shut off and will not start can you tell me what could the problem. A mechanic is working on it from April until now and cannot find the problem. It has cost us over a million dollars and still not running
Just in case someone had something similar and can recommend. A VW golf car runs completely normal but with ABS flashing and another brake warning and ! lit. This is accompanied by three bleeps which will continue as I drive. Took it to my trusted local garage but they could only tell me it’s a error code with the ECU and just said take it to an official VW garage.
Bit stumped but if people think their might be hope in the module being repaired instead of replaced that would be helpful to know thanks in advance
You can usually drive with an ABS light on, but just know that the ABS system may not engage properly (or at all) if you need to stop hard. This means your tires may lock causing loss of control. It’s best to get the issue repaired as soon as you can.
I have a 2005 International 4300 DT466. I’ve been recently having problems related to the ECU. My truck just suddenly stopped accelerating and stalled out on me one day, it cranked but would not start and I had to get it towed. But then there’s some instances where it actually will start. Now I’m currently dealing with the speedometer not working and it’s been happening since last night. Do you think the ECU itself needs to be replaced or is it the wiring that needs to be replaced? Would it be easy for me to fix myself? Thank you.
It’s possible, but my guess is a bad ground somewhere. I don’t know if the problem is easy to fix since we don’t know exactly what the problem is. I would expect the troubleshooting and diagnostics part will be the hardest, and electrical troubleshooting can be very difficult depending on the issue. Typically ECUs, bad grounds, and sensors are easy to fix. Wiring might be a little trickier depending on what went wrong and where on the harness the problem is.
Check all your ground points to make sure the straps are clean and tight. Next, inspect the wiring to make sure none of the insulation has rubbed through. You may have to chase this one with a multimeter and the factory service manual to really narrow it down. Good luck on your search.
Hello, my issue should have been simple. 1987 Alfa Romeo Spider Veloce. Something happened at 45mph when the distributor shaft wobbled and destroyed the rotor and cap. Checked everything carefully with no other damage. Replaced the whole distributor. Now I get no spark from coil. Power and tested both side of replaced coil. At one point the fuel pump ran key no-engine off. Fixed. That was the Main Relay.
It ran briefly but sputtered. NO. 1 and 2 plug wires were crossed. Fixed. Still no spark. Could this be a bad ECU? It has passed all possible tests via shop manual. Am I missing something else?
I’m a little confused. How was it running if there is still no spark? Have you checked all your fuses?
I have 2014 model ford figo 1.4 duratorq tdci titanium diesel car.
Unable to start car with lock signal indication illumination continuously. Technician checked and found carbon formation in PCM/ECU connectors and clearing the carbon then the car got started but this problem is continuously reoccurring.
Please suggest which part to be replaced PCM or connectors
Are you sure that’s not something with the immobilizer? I assume that’s what the “lock signal indication” is for.
Great article. I totally agree with all symptoms. However, there might be one more and that’s weird gear shifts and different behavior of the vehicle.
Could be, but that’s more likely caused by a bad transmission control unit (TCU).
My MB didn’t have any issues or warning lights, one day it appeared to go into neutral for approx 2 minutes until I parked. When I started the car up again it worked perfectly.
I asked my mechanic what might of happened & he provided me with 2 transmission error codes & suggested I just take to MB to update the software.
MB had the transmission codes from my mechanic however instead of updating the software, they told me they purposely tried to cause a malfunction to see if it happened again – this caused a fatal error & they told me they had broken my car! Now they tell me if they cannot figure out what to do – I have to pay $3k + labour for a new ECM. How is this ethical – they broke the car should they not have some responsibility?
What were the transmission codes?
To diagnose a problem, you often have to be able to replicate it. If the car is under warranty, most dealerships won’t even touch the car unless they can replicate the issue.
It sounds like whatever replication process they did also broke something, hopefully related to the root cause. I would guess that whatever component broke was probably on its way out anyway since you were experiencing intermittent issues.
My golf 6 gti 2010 model starts and cuts off. this happens when it display the faulty steering, airbags and handbrake.
Sounds like an electrical issue, like a bad ground or poor connection to the battery. Check to make sure all your grounds are clean and tight. Same with the battery terminals, they should be clean and tight.
Some days my car runs normal. It’s an ’09 Chevy Cobalt LT. Other days the gauges on the dashboard will move back and forth sporadically, a light will turn on, the light looks like a car with a lock on it. Then it will have trouble accelerating and shifting, it’s an automatic. It would jerk every time it would shift and I would also have to put it in neutral to stop.
I’m not sure. Perhaps there’s an electrical issue causing several seemingly unrelated issues. I would take it to a mechanic and have them go through it.
I have a 2010 Honda CRV .. Don’t do a whole lot of driving . but when I do decide to get out my car will sputter a little to start, just drags a little, but once it starts it runs fine .. been told I need new Starter but hesitant to let anyone touch it. had bad experience with when I let certain well known company just change my oil and air filters and the screwed up by radio.. not sure who I can trust.
Ask around your community and you will probably find a few mechanically inclined individuals who can recommend a good shop to you. Maybe it’s the starter but it could be something else instead.
Good diagnostic work is worth every penny you’ll pay. It can save you thousands over a mechanic who likes to use the “parts cannon” to guess what the problem is.
Hi,I have do a Diagnostic scan on my nissan sentra 2000 16si and outcome reflect NOT EQUIP.The reason for the scan was my car was use lot of fuel….I have change the tps sensor,it do the same probleme.Can you maybe assist me with that matter ?
Was there a check engine light? If so, what was the code you found?
While driving, my doors were unlocking and locking then dashboard lights came on and off several times…vehicle did not stall but in fear I pulled over. This occurred 3 times within a half hour. I prayed and 2 hours later made it home without incident. This was yesterday…I live hour from anything. I’m stumped…module. Electrical, battery…this is a Chevy truck
It sounds like you have a short somewhere in the electrical system. If this is the case, it will be almost impossible to pinpoint the root cause without putting a multimeter on the truck.
If you like to DIY, you can try grabbing a multimeter and a repair manual with a wiring diagram, then start checking different circuits to make sure you’re getting reasonable numbers.
It’s also possible you have a bad ground. You could try checking all ground straps to make sure they are clean and tight. Make sure there is no corrosion on the ground straps or the battery terminals, as corrosion inhibits the flow of electricity.
Will it damage the ECU if starting the engine with other switches at ON position like the Air-condition, rear screen heater, radio etc or will it be better with all the other switches at OFF position when starting the engine?
No, it’s perfectly fine to start the car with the HVAC and radio switches in any position.
If your battery is low on charge, the vehicle may have a bit more trouble starting, especially if it’s been sitting for a while or you’re in a colder climate. The extra load may cause the starter to crank more slowly, or not at all. However, you shouldn’t have to worry about this at all with a healthy battery.
i have a problem of toyota rav4 2.2ad 4wd diesel engine, the car cranked but not starting i dont know the problem. i diagnosed it the code says C1210 and C1280 both said the Engine control system malfunction.
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.