ECU is an electronic control unit that controls all electronic operations of the engine. Sometimes it’s called a car computer. ECU is a computerized device in a vehicle that controls one or more of the engine’s functions, including air/fuel mixture, ignition timing, and idling speed.
It receives input from sensors throughout the vehicle and uses that information to make adjustments to the engine to optimize its performance and reduce emissions. In modern cars, the ECU is a critical component that helps to improve fuel efficiency and reduce emissions.
In most passenger cars, a tuning of ECU gives significant enhancement in performance. To increase power, torque, and top speed, an ECU reflash is quite popular.