engine control unit

Engine Control Unit (ECU) Symptoms, Function & Location

In Electric by Magnus Sellén6 Comments

engine control unitYour vehicle can experience a range of different problems if the engine control unit goes bad.

If the function of the engine control unit is not accurate, i.e. to record and interpret the sensor readings from various sensors and using the data to control different functions of the engine system, the performance of your vehicle can drastically drop and the fuel efficiency can be lost.

As a result, the overall power of your vehicle and the responsiveness of your driving commands are significantly reduced.

It can also increase the fuel consumption of your vehicle unnecessarily and create a lot more pollution, which can be a problem at the time you are having your vehicle’s emission testing.

The ECU system is also capable of optimizing the proper Oil conditions of your vehicle as well as the overall maintenance. Since it is an electronic device, it can go bad or fail due to various reasons, such as aging, contamination, accident or exposure to the water.

If it is damaged, the problem should be addressed as soon as possible in order to avoid trouble in the future.

Symptoms of a bad engine control unit

The ECU is a vital component in modern cars because without it the car can stop functioning. Therefore, it is best to get any ECU related work solved as soon as possible. Usually, an ECU failure is accompanied by some problems that are easily discernable if you know what to look for.

1. Check Engine Light flashes

The first sign of any problem will show up on your dashboard as a shining Check Engine Light. This light comes on when a sensor senses an irregularity in the system, forcing you to get your car checked out. However, there are times when the Check Engine Light comes on for no reason. Using an OBDII scanner can show you, with the help of codes, if and where the problem exists.

2. Engine Related Troubles

Another problem that can arise from ECU failure is the misfiring of your car’s engine. Since the ECU controls the workings of an engine, any problem with it will have a direct effect on the engine’s performance. The engine might stall and become undependable.

However, these troubles are inconsistent meaning they can show up and disappear the next moment. You can find these trouble codes with an OBD2 Scanner.

3. Fuel Economy Suffers

When the engine is not performing at peak output due to ECU failure other things like fuel economy will be affected. You might even experience loss in power while accelerating and because the engine is losing power at various intervals your engine will use up more fuel excrete clack smoke and reduce the life of your engine.

4. Difficulty Starting

This is perhaps the first thing you notice, but since ignition problems can persist due to other reasons such as cold weather you won’t give much notice to it. However, if you have constant problems starting your car, there is surely something wrong with your ECU.

SEE NEXT:  How to Reset your Oil Life percentage in your Honda

It is probably best to let a professional look at such a problem as they can expertly distinguish between an ECU related problem or any other problem.

Bad Engine control unit (ECU)Check Engine light On

Bad fuel economy

Rough acceleration

Rough Idle

Hard starting condition
Faulty Internal Parts inside engine control unit (ECU)Repair Engine Control unit

Replace Engine Control unit

What is an Engine Control Unit or ECU?

engine control unit insideThe engine control unit or ECU of your vehicle is the main component of your engine system that enables the use of all the other devices. It is also known as the powertrain control module, and it usually installed under the dashboard of your vehicle. Basically, it is an electronic unit that serves as a controller for a number of sensors and the actuators that are installed on the internal combustion engine of your vehicle.

The core function of the engine control unit engine control module is to effectively maintain the optimum engine performance and the fuel consumption of your vehicle.

It uses a series of various datasets generated by the sensors and interprets the results by manipulating the data for automatic calculations. A number of sensors transmit the data over to the control unit, which utilizes it to maintain the performance of the vehicle by applying multidimensional performance maps. It is further used to adjust the actuators of the engine.

The engine control unit is generally capable of regulating and controlling the best performance of air-fuel mixture, idle speed, fuel injection, and ignition timing automatically with the help of sensed data.

Previously all these parameters were mechanically regulated, which is now being computerized to handle these functions electronically. In several vehicles, the engine control unit can also control the fuel lines of the vehicle. In such cases, it is called the electronic engine management system of the EEMS due to the scope of its functions.

The fuel consumption and optimum mileage are optimized by electronically injecting the fuel according to the requirement of the combustion using stoichiometric calculations EEMS are entirely controlled and manipulated by the sensors and the actuators on which this system rely on.

Where is the engine control unit located?

The engine control unit is essentially close to the area where your engine is located. In many vehicles, it can be found under the vehicle’s dashboard right behind the glove compartment. However, the location of the engine control unit in different vehicles can greatly vary depending on the design of the vehicle.

Therefore, it is highly recommended that the user refers to the user manual or the service manual that is provided by the manufacturing company.

Solutions for an ECU Failure

engine control unitNo matter the number of problems, ECU failure is easy to solve and usually requires a few minutes to assess. However, solving car related problems no matter how big or small requires some mechanical work which is best left to a mechanic. But that shouldn’t stop you from making your own diagnosis.

SEE NEXT:  Symptoms of a Bad Ignition Relay, Function & Location

Invest in an OBDII Scanner

This piece of equipment can be found very easily in the market. There are various brands competing in the market but honestly, the best one is that which works for you and your vehicle. Why should you buy one yourself? That’s because when you take your car to the mechanic the first thing he/she will do is attach an OBDII scanner to your car to grab the problem codes.

The mechanic will charge you for this and for the repair he/she makes to your car, so you are better off buying a scanner yourself. Using a scanner is not rocket science either. You simply attach the scanner to the car via a cable and the car’s ECU will transmit a code to the scanner. This code can tell you exactly where the problem lies, so when you go to the mechanic you can tell them the code and ask them to work on solving the problem directly.

You can find a good OBD2 scanner here on Amazon: OBD2 Scanner

Trial & Error Will Help You Learn

Sometimes you can learn about any ECU related complexities just by the way your car behaves. This means, you won’t have to visit the mechanic workshop every time you see a Check Engine Light. All you have to do is use your own OBDII scanner, which will help you diagnose any ECU related problems and act on the problem.

Replacing/Repairing the Engine Control Unit

The engine control unit serves as a computer for your engine system. In case of a failure of the engine control unit, your vehicle may completely stop and you would not be able to start it. therefore, it is strongly advised to not wait once the problem is identified in the initial stages of the problem with the engine control unit.

You can either repair or replace the engine control unit. However, if you go for repairs you may have to go through a lot of trouble and you will require special tools and knowledge to repair the circuit and the electronic components of the engine control unit.

It is comparatively very different from repairing the other parts of your vehicle. On top of that after the repair, there is still not guarantee that it will function effectively and efficiently in future. Therefore, it is recommended that you chose the option of replacement in order to save money as well as a lot of time that you may waste on repairing it and the stress that you will have to go through.

The replacement process is very easy as compared to the repairing. Here is a quick step by step guide on how you can go about replacing the engine control unit.

  1. Refer to the service manual to check and locate the engine control unit
  2. Once the problem is diagnosed, acquire all the tools you will need for the replacement along with the new engine control unit.
  3. Before you start to unplug the battery
  4. Clear the area for accessing the electronic control unit from the passenger compartment.
  5. Remove the brackets and the screws from the ECU
  6. Remove all the connections with the sensors and the electrical wires connected to the ECU.
  7. Remove the bolts if any and carefully take it out
  8. Replace the new ECU
  9. Tighten the bolts and put on the screws.
  10. Connect everything back to the original place, you may have to code the new engine control unit to your vehicle.
  11. Start your car and go for a test drive to check.
SEE NEXT:  How long does it take to fully charge a Tesla?

Engine Control Unit (ECU) Replacement Cost

The engine control unit or module is an essential component of your engine system and relatively a more sophisticated part. Therefore, the price of engine control unit replacement can be comparatively very high.

The engine control unit is like a brain of your engine management system without which all the actuators and sensors are rendered useless. It is to your car what motherboard is to your computer.

The replacement cost for the engine control unit for most vehicles on average is typically between $880 to $960, but it can be easily over the higher range point.

For some luxury vehicles, the price can go significantly higher than this average estimate. Apart from the cost of the parts, the labor involved for engine control unit replacement can be found for as low as $40 in some regions, while the mechanic can even charge you $130 or higher for this job. It depends a lot on the difficulty level of the vehicle, the mechanic you are dealing with and your location.

Diagnosis of the ECU

A dead or faulty ECU can be diagnosed by observing the symptoms of the failure at first. After that, a physical test will confirm that the part is not functioning properly. Here are the steps that you can follow:

  1. Observe if your engine is stalling or misfiring
  2. See if the performance of the engine is affected
  3. The ECU may have failed if you cannot start your car
  4. See if the check engine light is turned on.
  5. Get your multimeter and set it on the highest range
  6. Check for the readings after connecting the multimeter to the right connector on the ECU
  7. If the reading indicates zero value the ECU may have failed
  8. Test the electronic control unit using the multimeter only according to the instructions given on the service manual provided by the manufacturer.
  9. Be very careful and do not pass the current for more than a couple of seconds to avoid causing the damage that was previously not there
  10. Since the part is very sensitive and expensive, it is recommended to get it tested by the expert if you do not have enough knowledge as it can cause you more trouble.

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.

  1. Hi Magnus,

    My Audi A8 2011 went into limp mode a few seconds after I shifted into S gear and accelerated the gas and thus slowing down my car and having no breaking, Shifting or steering wheel control. My car would continue to have power running but not the engine. I tried many things to get my car to restart but it wouldn’t. So I had my car towed to an Audi dealer on the parking lot overnight. The next day they didn’t have a report for me but on the second day I did get the report with the recommendation to rebuild/replace the engine for over $23k with no reasons for what happened or explanations. With a new battery for over $500. They told me that they couldn’t tell me what issues are going on with my engine unless they open it up. There were no pricing for the labor or estimation of hours. I know I’m not being told the truth and being taken advantage of. A year ago they told 2 new front tires is over $700 in this new report they quoted me $90. A year ago an alignment was $189 and now it’s $229. Last year they replaced the a venthose and a valve. Please let me know what you think. I’m reluctant to let another Audi workshop service my car. Thank you.

  2. I lost my Key.Brought my 1999 rx 300 too a Lexus Dealer.Too get a New key cut.Informed me that i have too get another ECU Module.Due too not being able too Program a new Key for my Ignition.My car was working fine before i got it Towed there due too not having a Key.And needing a New Key as i lost mine.Why would i need too buy a New ECU ?

  3. I have a 2011 Dodge Durango Crew that’s having electrical problem. I started it up and it started making a wineing or huming sound accompied with a burnt wire smell. After that occurred it stopped running and would not start up. No interior lights, no information center lighting no lighting at all. It wouldn’t release the key and was stuck in park. Could you please help with this situation. Thanks

  4. My 09 Chevy Aveo quit taking gears what is the problem with my car it is automatic with a 4 cylinder motor front wheel drive

  5. Due to a very high demand and high ammount of comments, you have to wait for some time for your car questions to get answered. If you want to get fast answers from a certified master technician you can ask your questions here:
    Ask A Mechanic

Leave a Comment