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.

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

The Standard Body Module (SBM) controls many vehicle functions. These functions include audible warnings (chime), heated seat, ignition switch position reporting, interior and exterior lighting, rear compartment release, rear defogger control, Retained Accessory Power (RAP) control, seat belt warning control and steering wheel controls.

The SBM communicates with other systems over the class 2 serial data line (Purple wire at DLC connector terminal No. 2) 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.

Other modules that communicate with the SBM over this line are the Driver Door Module (DDM), Electronic Brake Control Module (EBCM), Heater and A/C Programmer Module (HCM), Instrument Panel Cluster (IPC), Memory Seat Module (MSM) if equipped, Powertrain Control Module (PCM), Pass-Key III® Vehicle Theft Deterrent Module (VTD), Remote Function Actuator (RFA) and the inflatable restraint Sensing and Diagnostic Module (SDM).

The Simple Bus Interface (SBI) (Light Blue wire) is used for communication between Driver's Door Module (DDM), Passenger Door Module (PDM) and Rear Door Module (RDM). SBI does not communicate with scan tool through the Data Link Connector (DLC). SBI information is interpreted by the DDM and reported on the class 2 data line. The Entertainment and Climate control (E & C) serial data line (Dark Green wire at DLC connector terminal No. 14) is used to communicate with radio, CD player and Heater and A/C Programmer Module (HCM).

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.

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 switch operation, door jamb switch operation, door lock switch operation, a RFA signal, inadvertent power transition, key-in-ignition switch, exterior lighting on, battery disconnect/reconnect condition or ignition switch is turned to RUN 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.

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.