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What is an Engine Control Module

An Engine Control Module or Electronic Control Module (ECU) is a term for any unit inside of a larger mechanical/electrical system.

It has a very definite purpose in your automobile and acts as the brain for your car, in fact, some people call it the brain box.

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ECU’s are generally used to monitor and control various engine functions. One function of the engine control module is determining what position the gas pedal is at at idle. This allows the car to know when you step on the accelerator, and how much gas it needs to feed the engine based on the amount of throttle you’re giving it.

Before switching to this system, cars used a mechanical throttle, where the accelerator was connected to the engine via a cable that regulated the injection of fuel.

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The ECU also controls our transmission, telling the car when to switch gears while driving. It can also adjust the gear ratio depending on what setting we put it in, reverse, drive, overdrive, or sport. In some car models, electronic control modules even have specialized settings for adverse or wintry weather conditions. Unfortunately this means that when an ECU becomes faulty, some major problems can occur.

Since one of the primary functions of an ECU is monitoring a series of car functions to register any errors with how it is operating, if an error is detected the ECU will generate a trouble code. Once the ECU notices the problem and generates the code, it will cause your cars Check Engine Light to come on. Once you notice that your Check Engine Light is on, you should take your car in to have it examined by a mechanic.

The mechanic will hook your ECU up to an OBD code scan tool like the Autel MaxiScan MS300 CAN Diagnostic Scan Tool for OBDII Vehicles, and will register any OBD error codes that it may be sending. At this point they will inspect the location of the error and advise you of any ECU repairs necessary.


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Unfortunately if your ECU is malfunctioning you might need to have the ECU repaired or replaced. If you have car issues resulting from faulty ECU’s, the garage or dealership is most likely going to reprogram or repair the ECU. This should solve the problem as long as the problem isn’t with your ECU. If your ECU is damaged or the motherboard is corroded you will need a total replacement.

If you are unlucky enough to need to have the ECU totally replaced, you are looking at quite a bill. Since the average cost for a new ECU is running around $1,500 per unit, but refurbished ECU’s can cost less. Quality refurbished ECU’s can be found by searching online or your mechanic will call his remanufactured ECU supplier to get a quote for you.




ECU’s are integral to the operation of modern cars. These are not simple mechanical devices that you should attempt to repair on your own. Make sure that if you are experiencing any problems with your ECU you take it in to a mechanic as soon as possible.

And if you are told that the issue is with your ECU get a second opinion, as this is a high ticket item for most car repair garages.

If you are looking for an ECU to purchase, Amazon has pretty much every ecu you may need.

Type in your part number in the Amazon search bar and you will generally be able to find a part from a reliable supplier.