An engine control unit (ECU) is an electronic control unit which controls various aspects of an internal combustionengine’s operation. The simplest ECUs control only the quantity of fuel injected into each cylinder each engine cycle. More advanced ECUs found on most modern cars also control the ignition timing, variable valve timing (VVT), the level of boost maintained by the turbocharger ( in turbocharged cars ), and control other peripherals.
An engine control unit (ECU), also known as power-train control module (PCM), or engine control module (ECM) is a type of electronic control unit that determines the ammount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. It does this by reading values from multidimensional maps which contain values calculated by sensor devices monitoring the engine.
Before ECUs, fuel injection, ignition timing and idle speed were directly controlled by mechanical and pneumatic sensors and actuators.