engine control unit

Engine Control Unit (ECU) Symptoms, Function & Location

In Electric by Magnus Sellén8 Comments

engine control unit

Your vehicle can have a number of different problems if the engine control unit is defective.

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

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

It can also unnecessarily increase your vehicle’s fuel consumption and cause much greater pollution, which can be a problem at the time of your vehicle’s emission test.

The ECU system is also able to optimize the correct oil condition of your vehicle and all maintenance. Since it is an electronic device, it can become faulty or fail for various reasons, such as aging, pollution, accident, or exposure to water.

If it is damaged, the problem should be repaired as soon as possible to avoid problems in the future.

Symptoms of a bad engine control unit

The ECU is an important component in modern cars, because without it the car cannot function. Therefore, it is best to solve all work related to the ECU as soon as possible. Normally, an ECU failure is associated with a number of problems that are easy to spot if you know what to look for.

1. Check Engine Light Flashes

The first sign of a problem is displayed on your dashboard as a glowing “Check Engine Light“. This light comes on when a sensor detects an irregularity in the system that forces you to have your car checked. However, there are times when the Check Engine Light will light up for no reason. Using an OBD2 scanner can show you if and where the problem exists using codes.

2. Engine Related Problems

Another problem that can be caused by a failure of the ECU is the backfire of your car’s engine. Since the ECU controls the operation of an engine, any problem with it will directly affect the performance of the engine. The engine could stall and become unreliable.

However, these problems are inconsistent, i.e. they can appear and disappear in the next moment. You can find these error codes with an OBD2 Scanner.

3. Fuel Economy Suffers

If the engine does not perform at peak power due to ECU failure, other things such as fuel consumption are affected. There may even be a loss of power when accelerating, and as the engine loses power at various intervals, your engine will consume more fuel, emit clear smoke, and reduce the life of your engine.

4. Difficulty Starting

This may be the first thing you notice, but since ignition problems may persist for other reasons, such as cold weather, you won’t give it much thought. However, if you constantly have problems starting your car, there is certainly something wrong with your ECU.

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It is probably best to have such a problem investigated by a specialist, as he will be able to distinguish between a problem with the ECU and another unrelated problem.

ProblemSymptomsCausesSolutions
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 inside

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

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

It uses a number of different data sets generated by the sensors and interprets the results by manipulating the data for automatic calculations. A number of sensors transmit the data to the ECU, which uses the data to maintain vehicle performance by applying multidimensional maps. It is also used to adjust the actuators of the engine.

The engine ECU is generally capable of automatically regulating and controlling the best performance of the air-fuel mixture, idle speed, fuel injection and ignition timing using the data acquired.

In the past, all these parameters were regulated mechanically, but this is now being computerized to handle these functions electronically. In several vehicles, the engine control unit can also control the vehicle’s fuel lines. In these cases, it is called the electronic engine management system or EEMS because of its range of functions.

Fuel consumption and optimum mileage are optimized by electronic fuel injection according to the requirements of the combustion process using stoichiometric calculations. The EEMS is fully controlled and manipulated by the sensors and actuators on which the system is based.

Where is the engine control unit located?

The engine control unit is essentially located near the area where your engine is located. In many vehicles, it is located under the dashboard of the car directly behind the glove compartment. However, the location of the engine control unit can vary greatly in different vehicles depending on the design of the vehicle.

It is therefore strongly recommended that the user refer to the owner’s manual or service manual provided by the manufacturer.

Solutions for an ECU Failure

engine control unitRegardless of the number of problems, an ECU failure is easy to solve and usually takes a few minutes to assess. However, solving problems related to cars, no matter how big or small, requires some mechanical work, which is best left to a mechanic. However, this should not prevent you from making your own diagnosis.

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Invest in an OBDII Scanner

This device is very easy to find on the market. There are different brands competing in the market, but honestly the best one is the one that works for you and your vehicle. Why should you buy one yourself? Because when you take your car to the mechanic, the first thing the mechanic will do is attach an OBDII scanner to your car to detect the problem codes.

The mechanic will charge you for this and for the repair he will do on your car, so it is better to buy a scanner yourself. Using a scanner is not rocket science either. You simply connect the scanner to the car via a cable and the ECU of the car will transmit a code to the scanner. This code can tell you exactly where the problem is. So if you go to the mechanic, you can tell him the code and ask him to work directly on solving the problem.

You can find a good OBD2 scanner here on Amazon: OBD2 Scannerir?t=askamastermec 20&l=am2&o=1&a=B01MR7FZS1

Trial & Error Will Help You Learn

Sometimes you can learn something about the complexity of ECUs just by the way your car behaves. This means that you don’t have to go to the mechanic’s workshop every time you see a check engine light. All you have to do is use your own OBD2 scanner to help diagnose ECU-related problems and respond to the problem.

Replacing/Repairing the Engine Control Unit

The engine control unit serves as a computer for your engine system. If the engine control unit fails, your vehicle may come to a complete standstill and you may not be able to start it. It is therefore strongly recommended that you do not wait once the problem is detected.

You can either repair or replace the engine control unit. However, if you choose to repair it yourself, you may face a lot of hassle, and you will need special tools and knowledge to repair the circuitry and electronic components of the engine control unit.

This is comparatively different from repairing the other parts of your vehicle. In addition, once repaired, there is still no guarantee that it will function effectively and efficiently in the future. It is therefore advisable to choose the replacement option to save both money and a lot of time that you might otherwise waste on the repair and the associated stress.

The replacement process is very simple compared to the repair. Here is a short step-by-step guide on how to replace 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, 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.
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Engine Control Unit (ECU) Replacement Cost

The engine control unit or module is an essential part of your engine system and a relatively sophisticated part. Therefore, the cost of replacing the engine control unit can be quite high.

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

The average cost of replacing the engine ECU for most cars is between $880 and $960, but can be slightly more than that.

For some luxury cars, the price can be well above this average estimate. Apart from the cost of the parts, in some areas the work involved in replacing the engine control unit can be as little as $40, while the mechanic can charge you $130 or more for this work. It depends greatly on the difficulty 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 first observing the symptoms of the failure. Then a physical test is performed to confirm that the part is not functioning properly. Here are the steps 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.

8 thoughts on “ Engine Control Unit (ECU) Symptoms, Function & Location ”

Comments
  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. Hi. My car emmits a black smoke from the exhaust. The mechanic told me the ECU is bad and needs an urgent replacement. Can a bad ECU cause a black smoke emission?

  6. Hi, my Lexus car emmits a black smoke from the exhaust and the fuel consumption is very high. The mechanic said my car ECU is the cause and it needs to be replaced. I wonder if a bad ECU can cause a car to emmit a black smoke?

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