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What is the ECU in a car?

Stephen Wright, 11 months ago

4 min read

  • Advice
  • Repair
ecu 0

The WhoCanFixMyCar guide to the Engine Control Unit (ECU) including average repair costs

Your ECU (engine control unit) is the part responsible for controlling key functions of a car engine. If something is not working correctly with the engine control unit (or a warning light flashes), serious problems could arise.

If you think that you need an ECU repair you can get a range of free quotes from trusted local mechanics using WhoCanFixMyCar.

Alternatively, if you suspect that you might have a problem with your car ECU, but aren't quite sure what it is, we have produced this simple guide to help you understand everything involved with an ECU repair and ECU remapping.

What is an ECU?

An engine control unit (or ECU) is responsible for running engine systems and functions.

Sensors throughout the car engine feed into the ECU, which processes the information they provide.

For example, there is a sensor in the catalytic converter that monitors the level of oxygen in the exhaust system.

The ECU processes readings provided by the sensors and makes the driver aware that there is a problem by switching on the engine management light.

The ECU will also change how the engine operates if required, for example, if the amount of oxygen getting into the engine is too low, an adjustment will be made to get more into the system by the control unit.

Repairing an ECU

If something has gone wrong with the control unit, the problem may be to do with an electrical wiring fault.

For example, the ECU may be telling you that the DPF is blocked, however, the DPF may be brand new and there is a very low chance the DPF is actually blocked. However, the sensor telling the ECU may be giving a bad reading or the wiring may be worn.

Sensors in the exhaust system can also become blocked and give false readings which effect the control unit's ability to deliver the correct information to a driver.

If there is an issue of this nature, a mechanic will take a reading from the ECU to find out what it thinks the problem is, before checking for themselves. If the engine control unit is not accurate, a repair will be required for the sensor or wiring. If it is correct, the fix will need to be made to the part.

It's impossible for a driver to tell whether the problem is real or not until the car is taken to a garage for inspection.

What is ECU remapping?

Having an engine control unit remapped involves changing the settings of the onboard computer. Some drivers request this work to be carried out in order to change the performance of the car engine. Car manufacturers set the computer to be uniform in each model, however, they can be changed to get a different output from an engine. Remapping is also known as reflashing or chipping.

ECU repair costs*

If you would like to find out if your car's engine control unit is faulty, you can book it in for inspection with a great local garage using WhoCanFixMyCar. Simply enter your vehicle registration and we'll get quotes from mechanics in your local area.

Average Cost of ECU Repair by Manufacturer
Audi£240.15
BMW£155.71
Ford£197.31
Peugeot£153.42
Vauxhall£129.54
Volkswagen£88.00

*This table uses data from quotes provided on WhoCanFixMyCar between 01/07/2021 and 29/09/2021