GM Service Manual Online
For 1990-2009 cars only
Table 1: Miscellaneous Functions

This vehicle is equipped with a Body Control Module (BCM). The BCM performs multiple body and engine control functions. The following vehicle systems are directly connected to the BCM:

    • Retained Accessory Power (RAP)
    • Audible warnings
    • Interior lighting
    • Door locks
    • Keyless entry
    • PASS-Key® II theft deterrent
    • Trunk Release

This vehicle also has the following systems:

    • Powertrain Control Module (PCM)
    • Electronic Brake Traction Control Module (EBTCM)
    • Instrument Panel Cluster (IPC)

These vehicle systems communicate with each other on an interconnecting bus, known as the Class 2 serial data link.

Some electrical components are directly connected and controlled by their system module. Other systems accomplish this feature by sharing data information with other systems on the Class 2 serial data link in order to execute various vehicle functions. All of the system data information (sensors, switches, etc.) may be monitored by any system module that completes the computer system.

All systems on the Class 2 serial data link use a communication process similar to a telephone system. Large amounts of information may be exchanged on a single data wire.

Communications between each system is accomplished by sending a digitally coded message. The digitally coded message consists of specific information a system module must follow. Each system module is assigned a recognition code (address). When a message is sent out on the Class 2 serial data link, the BCM provides more accurate and reliable computer system control functions. The BCM uses information from other systems in order to execute some functions. Before further diagnosis, review the following general information:

    • The BCM computer system operation
    • The system interactions with the BCM

Review this information in order to gain the following benefits:

    • Save diagnostic time.
    • Avoid misdiagnosis.
    • Prevent unnecessary parts replacement.

BCM Functions

The Body Control Module (BCM) is capable of accomplishing multiple body control functions Components directly connected to the BCM are controlled by the BCM's outputs. The BCM controls the outputs based on the following information:

    • The input information obtained from the sensors and the switches that are directly connected to the BCM
    • Borrowing information from other vehicle systems that are connected to the Class 2 serial data link

The BCM evaluates this information and controls the certain body systems by commanding an output on or off.

The BCM is also capable of commanding other vehicle systems to control functions that are not directly wired and/or controlled by the BCM. The BCM accomplishes this task by sending specific messages on the Class 2 serial data link. The vehicle system capable of performing such function will respond to the BCM message.

The BCM performs the following functions:

    • Retained Accessory Power (RAP)
    • Audible warnings
    • Interior lighting
    • Automatic power door locks
    • Keyless entry
    • PASS-Key® II theft deterrent
    • Trunk release

Retained Accessory Power (RAP)

The Retained Accessory Power (RAP) feature allows the operation of the following functions for 10 minutes (or until a vehicle door opens) after the ignition switch has been turned from the RUN or ACC to the LOCK or OFF position:

    • The radio
    • The power windows
    • The power sunroof (if equipped)

Refer to Retained Accessory Power (RAP) Circuit Description in Retained Accessory Power (RAP) for more information.

Audible Warnings

The Audible Warnings system performs the following functions:

    • Key in ignition reminder
    • Fasten seat belt reminder
    • Fasten belts indicator control
    • Parking brake reminder
    • Turn signal reminder
    • Low fuel reminder
    • Headlamps ON reminder
    • Last door closed locking confirmation
    • Feature customization

Refer to Audible Warnings Circuit Description in Instrument Panel, Gauges and Console for more information.

Interior Lighting

Interior Lighting system performs the following functions:

    • Interior illumination control
    • Delayed illumination
    • Exit illumination
    • Theater dimming
    • Keyless entry unlock illumination
    • Inadvertence load (battery rundown) protection

Refer to Interior Lights Circuit Description in Lighting Systems for more information.

Backup Lights

Automatic Door Locks

The Automatic Door Locks system performs the following functions:

    • All door unlock
    • All door lock
    • Last door closed locking
    • Lockout prevention
    • Lockout prevention override
    • Shift into PARK unlock
    • Shift out of PARK lock
    • All door relock
    • Remote driver door unlock
    • Remote all door unlock
    • Remote all door lock
    • Trunk Release
        Opens the rear compartmeny

The BCM provides feature customization of these door lock functions:

    • Shift out of PARK lock
    • Shift into PARK unlock
    • Last door closed locking

Refer to Power Door Locks Circuit Description in Doors for more information.

Keyless Entry

The Keyless Entry system performs the following functions:

    • Remote driver door unlock
    • Remote all door unlock
    • Remote all door lock
    • Remote activation verification
    • Remote alarm
    • Feature customization of remote activation verification
    • Trunk Release

Refer to Keyless Entry System Circuit Description in Keyless Entry for more information.

PASS-Key® II Theft Deterrent

The Personal Automotive Security System (PASS-Key® II) is a vehicle theft deterrent system. The PASS-Key® II is designed in order to prevent vehicle theft by disabling the engine from starting unless an ignition key with a specific resistor pellet code is used in the ignition lock cylinder.

The ignition lock cylinder contains the resistor sensing contacts. These contacts touch the resistor pellet embedded in the ignition key. When the ignition key is inserted in the ignition lock cylinder, the resistor pellet completes the key detection circuit (CKT 1073 and CKT 1074).

When the ignition switch is turned from the OFF to the RUN position, the BCM applies a 5 V reference voltage to CKT 1073. The BCM reads the resistor pellet code and compares the stored resistor pellet code against the ignition key resistor pellet code for a correct match.

Upon detecting a correct match, the BCM sends a fuel enable password to the PCM through the Class 2 serial data link. As a result, the PCM enables the theft deterrent relay. This action allows fuel delivery to the engine.

If the key resistor pellet is incorrect, the PCM performs the following actions:

    • Disables the theft deterrent relay
    • Stops fuel delivery to the engine

This vehicle disable period state lasts approximately 3 minutes. The SECURITY indicator flashes when the ignition switch is turned to the RUN position. Disconnecting the battery will not clear the timer sequence. The timer sequence resumes when the battery power is restored. If a proper key is inserted during the vehicle disable period, the vehicle will not start until the 3 minute time period elapses. After the 3 minute time period, the SECURITY indicator changes from a flashing state to a solid ON state. At this time, the BCM enters the theft deterrent re-learn mode. The engine will start if the correct ignition key resistor pellet is used.

Refer to Content Theft Deterrent (CTD) Circuit Description in Theft Deterrent for more information.

Miscellaneous Functions

Function

Description

BRAKE Indicator Lamp Control

The BCM controls the state of the BRAKE indicator lamp based on the status of the parking brake switch by sending a message to the IPC via the Class 2 serial data link.

Door/Trunk Ajar Indicator Lamp Control

The BCM controls the state of the Door/Trunk Ajar indicator lamp based on the status of the door and the rear compartment lid input switches by sending a message to the IPC via the Class 2 serial data link.

Fog Lamp Enable Control

The BCM controls the fog lamp operation based on the status of the ignition switch.

Day/Night Mode Sensing

The BCM determines the ambient light operating mode from the Daytime Running Lamp (DRL) control module. The BCM communicates this information to the IPC and the PCM via the Class 2 serial data link.

Traction Control Switch

The BCM receives a ground signal from the Electronic Traction Control Switch.

Twilight Sentinel Control

The BCM turns on the headlamps at night for 90 seconds when the following conditions occur:

    • The ignition switch is turned from the RUN position to the LOCK or the OFF position.
    • The headlamps switch is in the OFF position.
    • The headlamps are ON due to the night mode of the auto headlamp control.

Transaxle Shift Select Function

The BCM communicates the status of the transaxle shift select switch to the PCM and the IPC via the Class 2 serial data link.

BCM Wake-Up/Sleep State

The BCM performs these functions in the wake-up state. The BCM enters the sleep state when the following conditions exist:

    • Active control of system malfunctions stops.
    • Active monitoring of system malfunctions stops.
    • The BCM is idling.

The BCM must detect certain wake-up inputs before the BCM enters the wake-up state. The BCM monitors the inputs during the sleep state. This condition allows the BCM to switch between the awake state and the sleep state.

The BCM enters the wake-up state when receiving activity on any of the following inputs:

    • The instrument panel dimmer switch
    • The door lock (ajar) switch
    • The door lock switch
    • A keyless entry system signal
    • An inadvertent power (battery rundown) protection transition
    • The ignition switch in one of the following positions:
       - LOCK
       - OFF
       - RUN
       - ACC

The sleep state occurs when the following conditions exist:

    • The BCM stops active control of the system functions.
    • The BCM stops active monitoring of the system functions.

When the BCM detects a wake-up condition, the BCM enters the wake-up state. The conditions listed above are called Wake-Up Inputs. These wake-up inputs cause the BCM to change from a sleep state to a wake-up state. The BCM then begins active control and monitoring. The BCM has the ability to monitor for these wake-up inputs in the sleep state.

The BCM enters the sleep state when all of the following conditions exist:

    • No activity exists on the Class 2 serial data link.
    • The ignition switch is in the LOCK or the OFF position.
    • The BCM is not commanding any outputs.
    • No delay timers are actively counting.
    • No wake-up inputs are present.

Power Requirements

The BCM has 3 main voltage feeds and 1 ground. CKT 2340 is used in order to provide power for the BCM's logic and internal driver operation. CKT 1540 provides power for the automatic door lock. CKT 240 provides power to the courtesy lights.

BCM Inputs

The following components provide direct input to the BCM. Other systems may use this input information in order to perform certain functions. Refer to Body Control System Schematics for BCM connector and terminal locations.

Input

Function

Accessory

This input determines when the ignition switch is in the ACC position and the RUN position.

BCM Ground

This input provides ground for the door lock operation.

BCM

This input provides voltage for the BCM operation.

Courtesy Lamp On

This input provides the driver with the ability to request the illumination of the vehicle interior.

Crank

This input determines when the ignition is in the CRANK position.

Door Ajar

This input provides the door ajar status.

Door Lock Switch (Lock)

This input provides the door lock switch request in order to lock the vehicle doors.

Door Lock Switch (Unlock)

This input provides the door lock switch request in order to unlock the vehicle doors.

Door Locks

This input provides the voltage for the door lock actuator operation.

Driver Door Ajar

This input allows certain chime functions when the driver's door is open.

Ignition 0

This input determines the ignition switch status.

Ignition 1

This input determines when the ignition is in the following positions:

    • RUN
    • Bulb Test
    • START

Ignition Key Read

This input reads the PASS-Key® II resistor pellet code.

Key In Ignition

This input determines when the key is fully inserted in the ignition key cylinder.

Park Brake

This input determines when the parking brake is applied.

Park Lamps Off

This input determines the headlamp switch position.

Performance Shift

This input provides an interface to the shift select switch that determines if the driver has activated the performance shift switch.

RFA Link

This input provides an interface allowing the transfer of keyless entry information from the Remote Control Door Lock Receiver (RCDLR).

Seat Belt Switch

This input determines when the driver's seat belt is unfastened.

Serial Data

This input provides an interface with the following components through the Class 2 serial data link:

    • The PCM
    • The EBTCM
    • The IPC

Traction Control

This input determines when the traction control switch is grounded.

Trunk Ajar

This input determines when the rear compartment lid is ajar.

BCM Outputs

The BCM directly controls the following outputs. Other systems may request the BCM to control these outputs for certain functions. Refer to Body Control System Schematics for BCM connector and terminal locations.

Output

Function

All Door Lock

    • When active, this output supplies voltage to the door lock actuators and locks the doors.
    • When inactive this output provides ground to the door lock actuators.

Back Up Lamp

This output sends a ground signal to the Backup Lamp Relay Coil when the ignition switch is in RUN. This action enables the backup lamp relay. The Back Up Lamps turn on when the following conditions exits.

The Back Up Lamp is enabled by the BCM.

Courtesy Lamps

This output supplies the voltage to the courtesy lights, providing an inadvertent load (battery rundown) protection.

Driver Door Unlock

This output supplies ground to the door lock relay. This action provides power to the driver door actuator and unlocks the driver's door lock.

DRL Link

This output provides an interface to the DRL control module. This condition provides the following functions:

    • Allows the BCM to determine the current ambient light operating mode
    • Activates the vehicle headlamps for alarm and twilight sentinel features

Fog Lamp Control

This output sends a ground signal to the fog lamp enable relay coil when the ignition switch is in the RUN position. This action enables the fog lamp relay. The fog lamps turn ON when the following conditions exist:

    • The fog lamp switch is in the ON position.
    • The fog lamp relay is enabled by the BCM.

Horn

This output sends a ground signal to the horn relay. This action sounds the horn.

Ignition Reference Low

This output provides a ground to the ignition key cylinder for the PASS-Key® II resistor pellet.

Passenger Door Unlock

    • When active, this output provides the voltage to the door lock actuators and unlocks the doors (except the driver's door).
    • When inactive, this output provides ground to the door lock actuators.

RAP Relay Drive

This output provides ground in order to energize the RAP relay.

RFA Link

This output provides an interface allowing the transfer of keyless entry information to the Remote Control Door Lock Receiver (RCDLR).

Serial Data

This output provides an interface with the following components through the Class 2 serial data link:

    • The PCM
    • The EBTCM
    • The IPC

Theater Dimming 1

This output supplies ground in order to activate the IP and door courtesy lamps.

Theater Dimming 2

This output supplies ground in order to activate the dome and the roof rail courtesy/reading lamps.

Truck Release

This output sends a ground signal to the Rear Compartment Lid Release Relay Coil when the vehicle is in the PARK position. This action enables the rear compartment lid release relay. The rear compartment opens when the relay in energized.