Body Control Systems: Description and Operation

BODY CONTROL SYSTEM DESCRIPTION AND OPERATION
The body control system consists of 3 modules and their associated electrical controls. These modules are as follows:
^ The Dash Integration Module (DIM).
^ The Instrument Panel Integration Module (IPM).
^ The Rear Integration Module (RIM).

Each module integrates input and output controls for many functional areas. The inputs and outputs are wired to the closest module to minimize the length and amount of the wiring used. All 3 modules communicate on the class 2 serial data circuit, allowing data to be shared among them, as well as with other class 2 modules on the vehicle as needed.

DASH INTEGRATION MODULE (DIM)
The DIM is wired to the class 2 serial data circuit. The various DIM input and output circuits are described in the corresponding functional areas as indicated on the DIM electrical schematics.

The dash integration module (DIM) functions include the following:
^ Control of exterior lamps.
^ Hood ajar switch input W/export.
^ Horn relay control for theft activation.
^ Interior lamps and incandescent dimming.
^ Low side temperature for the HVAC compressor.
^ Power moding control over class 2 serial data circuit.
^ Steering wheel controls.
^ Storage of the clock settings and, sending a message out on the class 2 serial data circuit in response to requests from other modules.

SERIAL DATA POWER MODE
On vehicles that have several control modules connected by serial data circuits, one module is the Power Mode Master (PMM). On this vehicle the PMM is the DIM. The PMM receives 4 signals from the ignition switch.

To determine the correct power mode the PMM uses the following circuits:
^ Accessory voltage
^ Crank voltage
^ Ignition 1 voltage
^ Off/Run/Crank voltage

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 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 check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, the modules will fail-safe to the RUN power mode. If the discrete ignition input is not active, 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.

DIM WAKE-UP/SLEEP STATES
The DIM is able to control or perform all of the DIM functions in the wake-up state. The DIM enters the sleep state when active control or monitoring of system functions has stopped, and the DIM has become idle again. The DIM must detect certain wake-up inputs before entering the wake-up state. The DIM monitors for these inputs during the sleep state, where the DIM is able to detect switch transitions that cause the DIM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense the power mode requested.

The DIM 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.
^ Door ajar switch.
^ Headlamps are on.
^ Hood ajar switch.
^ Ignition is turned ON.
^ Parklamps are on.

The DIM will enter a sleep state when all of the following conditions exist:
^ 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 these conditions are met the DIM will enter a low power or sleep condition. This condition indicates that the DIM, which is the PMM of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.

INSTRUMENT PANEL INTEGRATION MODULE (IPM)
The various IPM input and output circuits are described in the corresponding areas as indicated on the IPM electrical schematics.

The IPM functions include the following:
^ Ambient light sensor input and twilight delay input for headlights control.
^ Foglight switch inputs.
^ Front HVAC air delivery and temperature controls.
^ Fuel door and rear compartment lid release switch input.
^ Ignition switch headlight control.
^ Interior lamps switch input.
^ I/P dimmer switch input.
^ Key in ignition switch input from the ignition switch.
^ Traction control switch input.

REAR INTEGRATION MODULE (RIM)
The various RIM inputs and outputs are described in the corresponding functional areas as indicated on the RIM electrical schematics.

The RIM functions include the following:
^ Ajar switch and tamper switch inputs from the rear compartment lid.
^ Content theft deterrent.
^ Fuel door and rear compartment lid release controls.
^ Fuel level sensor input.
^ Heated seat controls.
^ HVAC blower control.
^ Park brake relay controls.
^ Rear defogger control.
^ Rear foglights control.
^ Retained Accessory Power (RAP) relay control.
^ Reverse control for the backup lamps and automatic day/night mirror.
^ Various controls for the interior lamps.