If you type "electronic control module," or its better-known acronym, ECM, into the search field, you'll be gently guided over to the ECU (engine control unit) page. Inside the ECM, there's a microprocessor that receives, interprets and reacts to sensor inputs as fast as they occur. And it's composed of hardware as a standard circuit board that's encoded with software It is also called as Powertrain Control Module or PCM which acts as brains of the engine management system.
ECU is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It controls the fuel mixture, ignition timing, variable cam timing and emissions control. It constantly monitors emissions performance via its OBD (Onboard Diagnostics) programming, and it oversees the operation of the fuel pump, engine cooling fan and charging system. It also interacts with the transmission controller (if separate), ABS/traction/stability control system, body control module, climate control module and anti-theft system. In short, the engine control module performs a wide variety of functions that are necessary to operate a vehicle