Body Control Module: Description

WARNING: Vehicle is equipped with air bag supplemental restraint system. Before attempting ANY repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in AIR BAG RESTRAINT SYSTEM article.

NOTE: The Body Control Module (BCM) may also be referred to as Body Function Controller (BFC).

The Body Function Controller (BFC), located below right side of instrument panel, performs the following functions: A/C compressor request, A/C cooling fan, exterior and interior lighting control, battery rundown protection, chime, gauge control, instrument cluster indicator control and theft deterrent.

BFC communicates with components using class 2 data line and Serial Peripheral Interface (SPI) data line. BFC acts as an interpreter for data communication between class 2 and SPI data systems. Class 2 data line is used by BFC to communicate with the following modules: Electronic Brake Control Module (EBCM) and Powertrain Control Module (PCM). Class 2 serial data uses the peer-to-peer method and message arbitration to manage data line traffic.

SPI is a 3-wire synchronous serial data link through which the BFC controls the instrument cluster. BFC interprets driver warnings sent by control module on class 2 data line, then sends a SPI data message to the instrument cluster. SPI data bus messages include: Fuel gauge position, temperature gauge position, oil pressure, low engine coolant, check oil, volts, ABS, high beam, low fuel, high temperature, washer fluid level low, CRUISE, BRAKE, SERVICE VEHICLE SOON, door ajar, seat belt, theft system, and PRNDL.

Signals that activate the BFC are known as "wake-up" signals. BFC wake-up signals include: door ajar switches; ignition switch actuation; inadvertent power; battery rundown protection; or Remote Control Door Lock Receiver activation when driver's door unlock switch is activated or trunk opened.