It might sound odd to say so about an inanimate object, but cars are pretty clever devices. Your car is almost certainly more sophisticated than anything else you own, designed to operate in all weathers and at extremes of temperature, to drive at high speeds, and to cope with variable road conditions – and then keep doing so for years or even decades.

One of the things that enables this sophistication is the car’s ECU, its electronic brain that controls how the engine (or in the case of electric vehicles, the motor) operates. It’s a fundamental component of the modern car.

But what is an ECU? In this guide, we explain what an ECU is and what it does, where in your car it might be located, what ECU “tuning” involves, and what happens if there’s a problem with your car’s ECU.

What is an ECU?

ECU stands for Electronic Control Unit – basically a computer that handles various functions in your car.

The first ECUs started appearing in cars when computer-controlled fuel injection became commonplace in the 1980s. In modern cars there’s often more than just one of them; there are ECUs covering all manner of functions, and most are interconnected. If one ECU is like a standalone computer, then a modern car is more like a network.

What does an ECU do?

The most important ECU in a car is the one that handles the powertrain. Even the very simplest combustion-powered modern cars use an ECU to control how they run – at a very basic level, the computer interprets the position of the accelerator pedal, then delivers the fuel needed to deliver the power the driver has asked for, the timing of the spark that ignites the fuel, and in a lot of cases, the timing of the valves that allow the fuel and air mixture into each cylinder, then allow the exhaust gases to escape.