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Body Control System



BODY CONTROL SYSTEM DESCRIPTION AND OPERATION

The body control system consists of a body control module (BCM) and its associated controls. Battery positive voltage is provided to the BCM from BFC/BATT fuse in the left hand instrument panel fuse block. The module ground is wired to ground G202. The BCM is wired to the class 2 serial data communication bus as well as discrete input and output terminals to control the functions of the vehicle body.

Serial Data Power Mode
On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). The body control module (BCM) is the PMM on this vehicle. The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the class 2 serial data circuit.

To determine the correct power mode the PMM uses the following circuits:
- Ignition 0
- Ignition 1
- Ignition 3

Fail-Safe Operation
Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the power mode master (PMM) fail to send a power mode message. The fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.

Serial Data Messages
The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to RUN. In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.

Discrete Ignition Signals
Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, battery positive voltage, the modules will fail-safe to the RUN power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.

BCM Wake-Up/Sleep States
The body control module (BCM) is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested. This would allow the BCM to enter a sleep state when the key is IN or OUT of the ignition.

The BCM will enter a wake-up state if any of the following wake-up inputs are detected:
- Activity on the serial data line
- Detection of a battery disconnect and reconnect condition
- The headlamps are ON.
- The ignition is turned ON.
- Key-in-ignition switch
- The park lamps are ON.

The BCM will enter a sleep state when all of the following conditions exist:
- The ignition switch is OFF.
- No activity exists on the serial data line.
- No outputs are commanded.
- No delay timers are actively counting.
- No wake-up inputs are present.

If all of these conditions are met, the BCM will enter a low power or sleep condition. This condition indicates that the BCM, which is the power mode master (PMM) of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.

Data Line Communications
The body control module (BCM) communicates on the following 2 separate data lines:
- Class 2 serial data comminutions-Refer to Data Link Communications Description and Operation.
- Serial peripheral interface (SPI)-The BCM acts as the master between itself and the instrument panel cluster (IPC).

The various BCM input and output circuits are described in the corresponding functional areas indicated on the BCM electrical schematics. The BCM functions include the following:
- A/C compressor request-Refer to Air Temperature Description and Operation in HVAC Systems - Manual.
- Remote function control-Refer to Keyless Entry System Description and Operation in Keyless Entry.
- A/C cooling fan
- Audio delay power-Refer to Radio/Audio System Description and Operation in Radio, Stereo, and Compact Disc.
- Exterior and interior lighting control-Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.
- Daytime running lamps (DRL)
- Automatic lighting control
- Fog lamps
- Interior lighting-Refer to Interior Lighting Systems Description and Operation in Lighting Systems.
- Battery rundown protection from inadvertent power-Refer to Interior Lighting Systems Description and Operation in Lighting Systems.
- Chimes-Refer to Audible Warnings Description and Operation in Instrument Panel, Gages, and Console.
- Key-in-Ignition
- Head Lamps On
- Seat Belt Not Fastened
- Turn Signal On
- Park Brake Warning
- Door Ajar Warning
- Check Gages
- Gage control-Refer to Instrument Panel Cluster (IPC) Description and Operation in Instrument Panel, Gages, and Console.
- Instrument cluster indicator control-Refer to Instrument Panel Cluster (IPC) Description and Operation In Instrument Panel, Gages, and Console.
- Theft deterrent-Refer to Theft Systems Description and Operation in Theft Deterrent.
- Engine coolant level sensing-Refer to Cooling System Description and Operation in Cooling System.
- Washer solvent level sensing-Refer to Wiper/Washer System Description and Operation in Wipers/Washer Systems.
- Key-in-ignition sensing-Refer to Audible Warnings Description and Operation in Instrument Panel, Gages, and Console.
- Seat belt use sensing-Refer to Seat Belt System Description and Operation in Seat Belts.
- Brake fluid level sensing-Refer to Brake Warning System Description and Operation in Hydraulic Brakes.
- Parking brake state sensing-Refer to Brake Warning System Description and Operation in Hydraulic Brakes.
- Rear compartment interface-Refer to Power Door Locks Description and Operation in Doors.
- Horn interface-Refer to Horns System Description and Operation in Horns.
- Door lock interface-Refer to Power Door Locks Description and Operation in Doors.
- Bulb check-Refer to Instrument Panel Cluster (IPC) Description and Operation in Instrument Panel, Gages, and Console.
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