An engine control module (ECM) is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance.
body control module or ‘body computer’ is a generic term for an electronic control unit responsible for monitoring and controlling various electronic accessories in a vehicle’s body. Typically in a car the BCM controls the power windows, power mirrors, air conditioning, immobilizer system, central locking, etc. (Wikipedia