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.
OPERATION
The PCM and BFC share hardware and software in order to controlA/C compressor clutch. The BFC performs the following software functions: Limits low speed compressor operation, prevents clutch slippage, monitors for overpressure, determines low ambient pressure and controls compressor clutch.
Battery rundown protection (or battery guard) feature provides protection from excessive battery drain caused by high current loads that are accidentally left on. When ignition is turned off, a timeout period is started. If odometer reads less than 15 miles, timeout period will last for 3 minutes. If odometer reads more than 15 miles, timeout period will last for 20 minutes. When timeout expires, inadvertent power output is turned off.
Each time ignition switch is turned from ACC to RUN position, BFC controls an instrument cluster bulb check for a calibrated amount of time. During this bulb check, all gauge indicators are moved at the same time and all indicators are lit.
When BFC activates an indicator in the instrument cluster, it may also produce a chime. The following chimes are provided: Oil pressure indicator, engine coolant temperature indicator, low fuel indicator, BRAKE indicator, SERVICE VEHICLE SOON indicator, CHECK OIL indicator, volts indicator, LOW WASH indicator, low coolant indicator, and door ajar.