Circuit assignments for the body control module (BCM) relating to device power:

DEVICE POWER

Battery voltage is supplied to the BCM by circuit 1640. This input is internally monitored by the BCM for proper operating voltage. The proper operating voltage range is from 9-16 volts.

GROUNDING

Ground for the BCM is by circuit 550 through the left instrument panel fuse block and left body ground splice pack/body ground.

POWER MODE

The BCM monitors ignition 1 voltage circuit 39, accessory voltage circuit 43, and the engine run flag (ERF). The ERF is a serial data message from the engine controller. The BCM determines the state of the ignition switch for all modules on the serial data link.

ECU MALFUNCTION

The BCM performs an electrically erasable programmable read-only memory (EEPROM) checksum as a part of its internal diagnostics as the BCM is operating. When the EEPROM checksum does not equal a predetermined value, DTC B1000 sets. The checksum is the contents of each memory location in EEPROM added together.

OPTION CONFIGURATION

The vehicle option content information must be entered as part of the BCM programming procedure. If the vehicle option content information is not included and programming procedure is completed, DTC B1001 will set.

Circuit assignments for the body control module (BCM) relating to device brake:

PARK BRAKE

When the park brake input circuit 1134 to the BCM is grounded, as when the parking brake is applied, the BCM will turn on the brake telltale by sending a serial data message to the instrument panel cluster (IPC).

If the vehicle is moving at greater than 5 km/h (3 mph) and the park brake input to the BCM is grounded, the BCM will sound the warning chime to notify the driver the parking brake is applied. DTC B0005 will set under these conditions.

Circuit assignments for the body control module (BCM) relating to communications:

CLASS II COMMUNICATIONS

The class II serial data circuit 1807 is used to communicate information between modules, for example the body control module and the engine controller.

Contained in each module's memory is a list of serial data messages that are important and should be received by the module. Also contained are the default actions to be taken by the module, if one of the important messages is not received in time. One of those important messages is the state of health (SOH) message. This message is sent by a module, if no other message needs to be sent, to let all the other modules on the serial data circuit know the sending module is working correctly.

Each time the ignition is turned ON, all the modules on the class II serial data circuit first learn the other modules connected to the class II serial data circuit. Modules are able to learn the other modules on the serial data circuit because each of the important messages has a source identifier as part of the message.

This process of learning by a module allows the module to know if it has lost communication with a specific module on the class II data circuit.

Circuit assignments for the body control module (BCM) relating to doors and locks:

DOOR LOCKING/UNLOCKING

Door locking/unlocking, by remote keyless entry (RKE) or driver/all door lock switches, is controlled through the BCM.

When a driver door unlock has been requested, the BCM switches circuit 694 to battery voltage. This energizes the driver door unlock relay which supplies power to the driver door lock motor. Grounding is achieved through the closed contacts of the all-door lock relay. Grounding is also achieved through the windings of the all-door lock motors and the all-door unlock relay.

When an all-door unlock has been requested, the BCM switches circuit 194 to battery voltage. This energizes the door unlock relay which supplies power to the all-door lock motors. Grounding is achieved through the closed contacts of the door lock relay. Grounding is also achieved through the winding of the driver door lock motor and the driver door unlock relay.

When an all-door lock has been requested, the BCM switches circuit 195 to battery voltage. This energizes the door lock relay which supplies power to all-door lock motors. Grounding is achieved through the closed contacts of the door unlock relay and the BCM.

Lock/Unlock power application is limited by the BCM to 7 seconds to protect lock motors.

ANTI-LOCKOUT

Refer to Locks and Security for further information.

DECKLID/LIFTGATE RELEASE

The decklid/liftgate release is controlled by the body control module (BCM) circuit 362 providing battery voltage to the release solenoid. The BCM limits the amount of time the solenoid can be activated to 9 seconds to prevent damage to the solenoid. Reactivation may not be allowed for as much as 30 seconds.

Release of the decklid/liftgate can be initiated by either the transmitter or the decklid/liftgate release switch. Activating the decklid/liftgate release switch provides battery voltage to circuit 1576. Because remote keyless entry is an internal function of the BCM, no additional external wiring is necessary for transmitter input to the BCM. Decklid/liftgate release is not allowed by the BCM when vehicle speed is detected. The BCM receives vehicle speed serial data from the engine controller.

The BCM also monitors the cargo lamp switch input circuit 737 to determine when the decklid/liftgate is open. When the input is active, the BCM sends a class II message to the cluster to turn the hatch ajar telltale. Function operates in ACC or RUN.

FUEL LEVEL

The BCM receives fuel level percentage data from the PCM. The BCM calculates the data and sends the results to the cluster class II to control the fuel gage deflection.

ODOMETER

The BCM calculates vehicle mileage from rolling count speed messages provided by the PCM over class II. The BCM stores the mileage in memory with a maximum number of 999,999. The BCM sends the value to the cluster over class II to display the vehicle mileage. If the BCM is dead and replaced in the field, the last value displayed by the cluster must be entered in the new BCM.

Circuit assignments for the body control module (BCM) relating to driver information:

LOW BRAKE FLUID

Under low brake fluid conditions, the brake fluid switch closes. When closed, the brake fluid switch grounds circuit 33. The BCM responds by sending a serial data message to the instrument panel cluster (IPC) to turn on the brake telltale.

INSTRUMENT PANEL TELLTALES

The following table shows the telltale controlled by the BCM.

Important: The security telltale, brake telltale, and the service wrench telltale are also controlled by other controllers.

The instrument panel gages are controlled by the body control module (BCM) via the serial data link to the instrument panel cluster (IPC).

The following table gives the information source for each gage:

The following audible warnings are contained within the BCM and are controlled by the BCM:

Circuit assignments for the body control module (BCM) relating to gearshift:

GEARSHIFT UNLOCK

The gearshift unlock solenoid is energized by the BCM switching circuit 1135 to ground. When energized, the gearshift unlock solenoid will allow shifting from PARK. A condition for shifting from PARK is that the foot brake must be applied. The BCM receives this information over the serial data link from the engine controller.

The BCM also monitors ignition 1 circuit 39 and accessory circuit 43 to determine if the ignition switch is in the RUN or ACC position.

Circuit assignments for the body control module (BCM) relating to heating and air conditioning:

REAR DEFROST

When the rear defrost input circuit 292 to the BCM is momentarily switched to ground, as when the rear defrost switch is pressed, the BCM will respond by grounding circuit 193, the coil of the rear defrost relay.

This action energizes the rear defrost relay providing power to circuit 293 - rear defrost heater elements, and circuit 193- rear defrost LED telltale. Momentarily switching circuit 292 to ground again will result in the BCM turning the rear defrost relay OFF.

The first time in an ignition cycle that the rear defrost is activated, rear defrost will remain ON for 15 minutes or until the ignition switch is turned OFF. If rear defrost is activated again during the same ignition cycle, rear defrost will remain ON for 7 1/2 minutes or until the ignition switch is turned OFF.

A/C REQUEST

A/C request is made by the HVAC control head supplying voltage to circuit 603 to the BCM. The BCM will then request over the serial data link to the engine controller to operate the compressor. The BCM provides evaporator freeze protection by monitoring engine speed and ambient temperature.

HVAC FAN HI BLOW CONTROL

The BCM controls the fan operation when the HVAC fan switch is on HI. The BCM supplies voltage to the HVAC blower relay coil over circuit 52. This will close the relay contacts and provide battery voltage to the blower motor without going through the blower motor resistors.

The retailer can also enable the BCM to provide an A/C afterblow function to eliminate odor associated with A/C usage. This function operates by running the HVAC fan for a few minutes, approximately 30-40 minutes, after the vehicle has been turned OFF, if the A/C has been used.

Circuit assignments for the body control module (BCM) relating to lighting:

DISPLAY DIMMING

Display dimming is controlled by the BCM based on input received from the dimming potentiometer. The dimming potentiometer is connected between circuit 719 and circuit 230. The BCM monitors these inputs and provides a pulse width modulated (PWM) output at circuit 8 to operate the display lamps.

PARK LAMP SWITCH

The BCM compares the state of the park lamp circuit 9 to the high beam headlamp circuit 1200 and the low beam headlamp circuit 1201.

If the park lamp circuit is grounded/open and either the low beam circuit is at battery voltage or the high beam circuit is grounded, DTC B2662 will set.

DAYTIME RUNNING LAMPS

Daytime running lamps (DRL) are controlled by the BCM based on input from the high beam headlamp circuit 1200, the low beam headlamp circuit 1201, the parking brake circuit 1134, and ignition switch state.

When DRL operation is desired, the BCM switches circuit 592 to ground. This action energizes the DRL relay. When energized, the DRL relay operates the left high beam headlamp and right high beam headlamp as a series circuit, one-half of battery voltage across each high beam headlamp.

When DRL operation is not desired, the BCM does not provide ground for the DRL relay. When not energized, as when high beam headlamps are desired, the DRL relay operates the right and left high beam headlamps as a parallel circuit, full battery voltage across each high beam headlamp.

For DRL operation, the parking brake must be fully released, the ignition switch must be in the RUN position and headlamp switch must be in the OFF position. On automatic transaxle vehicles, the vehicle must be shifted out of Park to activate the DRL's. Under normal operating conditions, the feedback voltage to the BCM measured at circuit 1200 is:

DOME/REAR READING LAMPS

Dome and rear reading lamp operation is through the body control module (BCM) providing ground to circuit 156. When manually operated by their respective local switches, the dome and rear reading lamps are grounded through circuit 450 and the right body ground splice pack.

BATTERY RUNDOWN PROTECTION

Important: If the dome lamp is not in the DOOR position the battery rundown protection feature does not function.

Battery rundown protection is controlled by the BCM when the dome lamp is in the DOOR position. If the dome lamp is on an extended amount of time due to a hatch being left open, the BCM will turn OFF the output for the dome lamp after 20 minutes to conserve battery energy. If the odometer is less than 24 km (15 miles), the dome lamp will be turned OFF in 3 minutes. When the odometer is over 24 km (15 miles), the timer will change to 20 minutes.

Circuit assignments for the body control module (BCM) relating to security system:

SECURITY SYSTEM

The passlock sensor is powered by circuit 1459. The passlock sensor is grounded by circuit 1835. Passlock sensor data is supplied to the BCM by circuit 1836.

The passlock sensor data supplied to the BCM is in the form of V-codes or voltage codes. When the proper ignition key is turned in the ignition switch, the correct V-code is supplied to the BCM. The BCM responds by sending a serial data password to the engine controller allowing the engine to run.

Under a tamper condition, a specific V-code is supplied to the BCM. The BCM will send a class II message to the PCM disabling the fuel injectors.

KEY-IN-IGNITION

When the ignition key is seated in the ignition switch, the key-in-ignition switch contacts close grounding circuit 80. The BCM monitors the state of the key-in-ignition switch, the state of the ignition switch (OFF, ACC or RUN) and the driver's door to control the key-in-ignition chime.

HORN

The BCM controls the operation of the horns for the security system and remote keyless entry (RKE) functions. Circuit 28 is grounded by the BCM when horn operation is desired. Normal operation of the horn is performed by the horn switch grounding the horn relay and is not controlled by the BCM.

There is a 30 second delay prior to setting DTC 2752 - Horn Relay Coil Circuit Low for grounded circuit conditions. It is possible to set DTC 2752 if the horn is operated by the horn switch for greater than 30 seconds.