What is an ECU?

An Engine Control Unit (ECU) also known as Engine Management System (EMS) is an electronic control unit which controls various aspects of an internal combustion engine's operation. The most simple ECUs simply control 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 Cam Timing (VCT), the level of Boost maintained by the turbocharger (in turbocharged cars), and control other peripherals.