An automotive BCM or body control module is designed to control and monitor various systems much like a typical PCM (power-train control mode). The BCM can be thought as a support computer for everything not power-train related such as the seat controls and memory, seat belt warning, vehicle security systems (including key fob operation), interior lighting, windshield wiper systems, headlight and DRL controls, rear window defroster, dashboard lighting, trunk, lift back, automatic sliding door controls, window controls, cruise control and shift interlock systems. It also shares data within the CAN (controller area network) to additional systems such as the climate control (HVAC), traction control, PCM (powertrain control module), ABS (antilock brake system), SRS (safety restraint system) and the instrument cluster. We use the term BCM but it is also know as a GEM (generic electric module), FCM (Front control module)
As with any computer, any component inside the unit can go bad such as a transistor, IC or resistor. Subject to vibration, heat, coldness and moisture the BCM is built to withstand these conditions to a certain point. Voltage surges and a low battery can also take their toll on the BCM.