Description & Operation

WARNING: Deactivate air bag system before performing any service operation. See appropriate AIR BAG RESTRAINT SYSTEMS article. Do not apply electrical power to any component on steering column without first deactivating air bag system. Air bag may deploy.

The Body Control Module (BCM) performs the following functions: reminder/warning audible warning functions, interior illumination/lighting control, automatic power door locking operations, keyless entry functions, Passlock(tm), Retained Accessory Power (RAP) and miscellaneous functions such as, BRAKE indicator light control, foglight, day/night mode sensing, overvoltage protection, transmission shift select, anti-theft, vehicle configuration storage, serial data communications, calibrations and DLC diagnostic operation.

BCM communicates with components using Class 2 serial data line. Class 2 serial data line is used by various systems to share data information with other systems in order to execute various vehicle functions. Communication between each system is accomplished by sending digitally coded messages, which consist of specific information the system module must follow. Each system module is assigned its own recognition code, so that it can respond to appropriate messages. The BCM can determine State Of Health (SOH) of other systems.

Signals that activate the BCM are known as "wake-up" signals. BCM can enter a sleep state when active control or monitoring of systems has stopped or when BCM is idling. BCM monitors its inputs during the sleep state, which allows BCM to switch between sleep and awake states. BCM is asleep when it is not controlling or monitoring the following wake-up inputs: instrument panel dimmer switch, door lock ajar switch, door lock switch, a keyless entry signal, inadvertent power (battery rundown) protection transition, or ignition switch is turned to LOCK, RUN or ACC position. The BCM will enter a sleep state when all of the following conditions exist: no activity on class 2 serial data line, ignition switch is turned to LOCK position, no outputs are commanded, no delay timers are actively counting and no wake-up inputs exist.

BCM control RAP feature. RAP feature allows operation of radio, power windows and power sun roof (if equipped) for 10 minutes, or until a door opens, after ignition switch turns from ON or ACC to LOCK position. BCM controls application of power through RAP relay. RAP relay controlled feed provides power to power windows and sun roof. Power to radio is controlled through class 2 serial data circuit. When BCM interrupts power to RAP relay control circuit, it sends a signal to radio over class 2 serial data circuit to shut off. BCM turns RAP relay off when ignition switch is in START position.

BCM has 3 main power feeds and 2 grounds. Power for BCM's logic and internal driver operation is supplied through circuit No. 2140 (Orange wire). Power for door lock system is supplied through circuit No. 1940 (Orange wire). Power for courtesy lights is supplied through circuit No. 240 (Orange wire).