Description & Operation

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

NOTE: The Body Control Module (BCM) may also be referred to as Standard Body Module (SBM).

The Standard Body Module (SBM) uses the class 2 serial data line to communicate with the following modules: Powertrain Control Module (PCM), Instrument Panel Cluster (IPC), Heating and A/C (HVAC) programmer, Electronic Brake and Traction Control Module (EBTCM), Driver Door Module (DDM), PASS-Key(R) III module, cellular telephone module, Remote Function Actuator (RFA) module, Sensing and Diagnostic Module (SDM) and Memory Seat Module (MSM). SBM can directly control various vehicle functions (i.e., brake shift interlock and interior dimming control) or send commands to other systems to command various functions.

Signals that activate the SBM are known as "wake-up" signals. These wake-up signals include: Any activity on serial data line; any accessory function; door handle, door jamb or door lock switch operation; an RFA signal; inadvertent power transition; key-in-ignition switch; exterior lighting on; battery disconnect/reconnect condition or ignition switch is turned to ON position. Multiple switch wake-up signals are necessary to sense insertion and removal of ignition key. This allows SBM to enter a sleep state when key is in ignition.

When SBM is not actively controlling or monitoring systems, it enters a sleep state. SBM will enter a sleep state when all of the following conditions exist: No activity on serial data line, ignition switch is in OFF position, no outputs are commanded, no delay timers are actively counting and no wake-up inputs exist.

Various components provide direct input to SBM, which uses this information or passes it on to other systems in order to control various functions. These components include: Accessory, auxiliary chime, CRANK, courtesy light switch, Ignition 0, Ignition 1, seat belt switch, trunk ajar switch, low coolant switch, washer fluid level switch, trunk lid release switch and heated seat status. SBM directly controls the following outputs: Foglight enable, theater dimming 1, theater dimming 2, inadvertent power, Light Control Module (LCM) link and RFA link.

SBM provides an overvoltage protection which prevents headlights from activating when system voltage is more than a certain level. SBM provides a Retained Accessory Power (RAP) function which allows certain systems (i.e., radio, power windows) to be operated after ignition switch is turned to OFF position. The RAP function is disabled after a 10-minute period or when any door is opened.