A body control module, or BCM, coordinates different operations within a car through the use of signals. Every electrical part of modern cars, from the door locks to the headlights, is controlled by a BCM.
BCMs are designed to make a car's operations simpler by controlling all electrical operations in one module. Older vehicles had various modules controlling these same tasks. While BCMs are helpful in eliminating excess modules, their main downfall is observed when they begin to malfunction. Every electrical operation in a vehicle could be faulty, from headlights not turning on to doors not locking, when a BCM needs to be replaced.