What is an ECU (electronic control unit)?

An ECU (electronic control unit) is a specialised computer responsible for making your car run properly. On modern cars, you'll usually find many separate ECUs controlling loads of different components such as the engine, gearbox, safety systems and on-board technology.

The first ECUs were needed as engines swapped from old carburettors to modern electronic fuel injection – the ECU would measure various data points across the engine to work out the perfect time to inject and ignite the fuel for reliable and efficient operation. Over time, more engine features became electronically controlled including 'fly-by-wire' throttle valves and variable-valve-timing systems – with each being incorporated into the ECU, enabling even greater control over an engine's performance.