Principles of Operation: Notes
WARNING: This page is about a different car, the 2013 Ford Fiesta. However, it is still accessible from the selected car via links, so may be relevant.
The Body Control Module (BCM) controls various systems by monitoring inputs from switches, sensors and messages sent over the Medium Speed Controller Area Network (MS-CAN) from other modules. The BCM activates outputs based on the inputs received. For example, the BCM monitors the headlamp switch position, and based on this input, the BCM may provide voltage to the exterior lamps.