Body Control System Buick Century VI

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Begin the diagnosis of the body control system by performing the Diagnostic System Check for the system in which the customer concern is apparent.

The Diagnostic System Check will direct you to the correct procedure for diagnosing the system and where the procedure is located.

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Scan Tool Data Definitions

Software Part Number: Part number of component program or the ECU. Used to determine applicability to vehicle RPO content.

Accessory 1: Input from ignition switch ACCESSORY circuit. Used to determine power mode. Hot in ACCESSORY and RUN.

Battery Power 2: Input showing the state of the Battery Power 2 circuit to the control module.

Battery Power 3: Input showing the state of the Battery Power 3 circuit to the control module.

Battery Voltage: The scan tool displays 0.0-16.0 volts. The battery voltage input represents the system voltage measured at the BCM ignition feed input.

Courtesy Ground: Input showing the state of the courtesy ground from the control module.

Crank: Input from ignition switch closed to B+ when the ignition switch is in the CRANK position.

Ground 2: Input showing the state of the Ground 2 circuit to the control module.

Ignition 0: Input to the control module from the ignition switch indicating the Ignition 0 position. Switch closed (HOT) in ignition switch positions Unlock, Accessory, Run, Crank

Ignition 1: Input to the control module from the ignition switch indicating the Ignition 1 position. Switch closed (HOT) in ignition switch positions Run, Crank

Key In Ignition: Input from ignition switch indicating that the ignition key is inserted into the ignition switch. HOT with key in ignition and ignition switch position LOCK.

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Circuit Description

The internal fault detection is handled inside the control module. No external circuits are involved.

Conditions for Running the DTC

The microprocessor runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

Conditions for Setting the DTC

1. The control module detects an internal write malfunction.
2. The control module detects an internal checksum malfunction.

Action Taken When the DTC Sets

The microprocessor refuses all additional inputs.

Conditions for Clearing the DTC

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

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1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

The internal fault detection is handled inside the control module. No external circuits are involved.

The module microprocessor must be active/awake.

This DTC indicates the KAM in the module has been reset. It is a normal occurrence when battery positive voltage or ground is removed from the module, such as a battery disconnect.

The microprocessor reverts back to the base programmed critical operating data until new data is learned and stored in KAM.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Scheme 31

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

As part of normal data processing, the module performs a data programming check on its writes to the electrically erasable read only memory (EEPROM). The EEPROM write error detection is handled inside the control module. No external circuits are involved.

The module runs the program to detect an EEPROM write error. The only requirements are battery positive voltage and ground. This program runs even if the battery positive voltage is out of the valid operating range.

The module writes information to a data block in the EEPROM. The module then reads the data and compares it to what was sent to the data block. If the data does not match after 3 consecutive attempts, the module sets the DTC.

The module writes to another area of the EEPROM, this becomes the new permanent area to store the data. The data location is allowed to change until all of the available EEPROM is used. If a B1004 DTC is also set, the module reverts to base operation values programmed for those blocks of data that have failed. The blocks of data that have not failed the checksum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

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1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

The electrically erasable programmable read-only memory (EEPROM) check sum error detection is handled inside the control module. No external circuits are involved.

The module runs the program to detect an EEPROM checksum error after each wake-up. The only requirements are battery positive voltage and ground. This program runs even if the voltage is out of the valid operating range.

The module retains an inverse copy of the digital value stored in certain blocks of memory in the EEPROM. The module then reads the information from those certain blocks and adds the stored inverse value to the current value. If they do not equal 0, the module sets the DTC.

The module reverts to base operation values programed for those blocks of data that have failed the check sum test. The blocks of data that have not failed the check sum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

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1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

The electrically erasable programmable read-only memory (EEPROM) check sum error detection is handled inside the control module. No external circuits are involved.

The module runs the program to detect an EEPROM checksum error after each wake-up. The only requirements are battery positive voltage and ground. This program runs even if the voltage is out of the valid operating range.

The module retains an inverse copy of the digital value stored in certain blocks of memory in the EEPROM. The module then reads the information from those certain blocks and adds the stored inverse value to the current value. If they do not equal 0, the module sets the DTC.

The module reverts to base operation values programed for those blocks of data that have failed the check sum test. The blocks of data that have not failed the check sum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

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1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

The battery feed circuit, from the DOOR LOCKS fuse to the BCM, provides power for the door locks.

1. The BCM must be powered.
2. The voltage on the battery feed circuit, from the DOOR LOCKS fuse to the BCM must be between 9-16 volts.

The BCM detects that the circuit from the DOOR LOCKS fuse to the BCM is less than 1 volt for 300 milliseconds.

The BCM stores DTC B1334 in memory.

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1. A current DTC B1334 will clear if the BCM no longer detects the fault.
2. A history DTC B1334 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

The battery feed circuit, from the INADV POWER BUS/RAP fuse to the BCM, provides power for the interior lamps.

The voltage on the interior lamps feed circuit from the BCM must be between 9-16 volts.

The BCM detects that the circuit from the INADV POWER BUS/RAP fuse to the BCM is less than 1 volt for longer than 300 milliseconds.

The BCM stores DTC B1339 in memory.

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1. A current DTC B1339 will clear if the BCM no longer detects the fault.
2. A history DTC B1339 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

The BCM's ground 2 circuit provides ground for the high current devices controlled by the BCM.

The BCM monitors the ground 2 at all times.

The BCM detects that the ground 2 circuit is not at ground potential for 300 milliseconds.

The BCM stores DTC B1354 in memory.

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1. A current DTC B1354 will clear if the BCM no longer detects the fault.
2. A history DTC B1354 will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.

The body control module (BCM) monitors the Ignition 0, Ignition 1, Crank and Accessory circuits from the ignition switch. The BCM uses the voltage state (B+ or 0) and the sequence of state changes to determine the power mode called for by the ignition switch. Refer to the table in BODY CONTROL SYSTEM DESCRIPTION AND OPERATION .

The BCM must be powered and must detect a change in the ignition switch circuit states.

1. The BCM detects an improper voltage on one of the ignition switch circuits.
2. One of the ignition switch circuits may be shorted to either B+ or ground.
3. The sequence of the change of the circuit may be incorrect for the expected power mode.

1. The BCM stores the DTC to memory.
2. The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the class 2 serial data communications circuits.
3. The other modules on the vehicle operate in a fail safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the class 2 serial data communications circuits.

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1. The current DTC will clear when the BCM detects a sequence of ignition switch inputs that match the expected power mode.
2. A history DTC will clear after 100 ignition cycles with no repeated malfunction.

The internal fault detection is handled inside the control module. No external circuits are involved.

The microprocessor runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

1. The control module detects an internal write malfunction.
2. The control module detects an internal checksum malfunction.

If equipped, the following module specific actions may occur

1. The ABS indicator turns on.
2. The BRAKE Warning indicator turns on.
3. The SERVICE 4WD indicator turns on and the system will be disabled.
4. The Service 4 Wheel Steering indicator turns on and the system will be disabled.
5. The SERVICE RIDE SYS or SERVICE RIDE CONTROL message is displayed.
6. The SERVICE SUSPENSION SYS message is displayed.
7. The TCS indicator turns on.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

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1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the body control system. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to TESTING FOR INTERMITTENT AND POOR CONNECTIONS in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

POWER MODE MISMATCH

Normal vehicle class 2 communications and module operations will not begin until the system power mode has been identified. Discrete wires from the ignition switch contacts are monitored by the power mode master (PMM) module in order to determine the correct power mode. The PMM communicates the system power mode to all class 2 modules on the class 2 serial data line. Refer to BODY CONTROL SYSTEM DESCRIPTION AND OPERATION to identify which module is the PMM and the applicable power mode look up table.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 6. This step tests for battery voltage on the signal circuits that are not required.
2. 7. This step tests for no battery voltage on the required signal circuits.
3. 8. If any ignition switch parameters that should be inactive in the present ignition switch position are active, 2 ignition switch signal circuits may be shorted together.
4. 9. This step eliminates open circuits as the cause of the malfunction.

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1. Disconnect the negative battery cable. Refer to «BATTERY NEGATIVE CABLE DISCONNECT/CONNECT PROCEDURE»(/buick/century/vi-1997-2005/remont/body-electrical/#battery) .
2. Remove the left instrument panel insulator. Refer to «CLOSEOUT/INSULATOR PANEL REPLACEMENT -- LEFT»(/buick/century/vi-1997-2005/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
3. Disconnect the BCM electrical connectors.
4. Push the BCM up and move the bottom of the BCM away from and out of the mounting bracket slot in order to remove the BCM.

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1. Push the top of the BCM up into the mounting bracket in order to install the BCM. Then, while holding the BCM up, engage the bottom of the BCM into the mounting bracket slot.
2. Connect the BCM electrical connectors.
3. Install the left instrument panel insulator. Refer to «CLOSEOUT/INSULATOR PANEL REPLACEMENT -- LEFT»(/buick/century/vi-1997-2005/remont/gauges-instrument-panels/#instrument-panel-gages-and-console) in Instrument Panel, Gages and Console.
4. Connect the negative battery cable. Refer to «BATTERY NEGATIVE CABLE DISCONNECT/CONNECT PROCEDURE»(/buick/century/vi-1997-2005/remont/body-electrical/#battery) in Battery.
5. Set up the new BCM. Refer to «BODY CONTROL MODULE (BCM) PROGRAMMING/RPO CONFIGURATION»(/buick/century/vi-1997-2005/remont/communication-devices/#body-control-system__body-control-module-bcm-programmingrpo-configuration) .

Body Control Module (BCM) Programming/RPO Configuration

During Body Control Module (BCM) related service, the procedures below are designated to set-up the BCM correctly. Before you start, read these carefully and completely.

1. Read this procedure carefully and completely.
2. The BCM will not function properly if the Setup New BCM procedure is not performed.
3. Make sure the battery is fully charged.
4. Make sure all disconnected devices and connectors are reconnected.
5. Perform the «PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS»(/buick/century/vi-1997-2005/remont/door-locks-anti-theft-systems/#theft-deterrent-system) in Theft Deterrent after successfully finishing the Setup New BCM procedure. If the «PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS»(/buick/century/vi-1997-2005/remont/door-locks-anti-theft-systems/#theft-deterrent-system) procedure is not performed after a BCM replacement, one of the following conditions will occur: The vehicle will not be protected against theft by the Passlock Sensor system. The engine will not crank nor start.

Setup New Body Control Module (BCM)

Note. After the procedure is completed, personalization of the BCM defaults to a default setting. Inform the customer that the personalization must be set again.

The following procedure will set up the new BCM

1. Connect a Tech 2 to the Data Link Connector (DLC).
2. Turn the ignition switch ON.
3. Select "Diagnostics" and input all of the required data to select the correct vehicle when prompted by the Tech 2.
4. Select "Body" and then "Body Control Module".
5. Select "Special Functions".
6. Select "New VIN" and follow the screen directions to input all required data.
7. Exit back to the "Special Functions" menu.
8. Select "BCM Reprogramming".
9. The scan tool will display "Do you want to setup a Body Control Module?" At the prompt, select "Setup BCM" soft-key on the scan tool.
10. The scan tool will display "Now setting up the new Body Control Module".
11. When the BCM has been setup successfully, the scan tool will display "Body Control Module setup is complete".
12. When the BCM Setup Procedure and VIN have been entered, proceed with the procedure «PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS»(/buick/century/vi-1997-2005/remont/door-locks-anti-theft-systems/#theft-deterrent-system) in Theft Deterrent.

Theft Deterrent

Perform the procedure PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS in Theft Deterrent.

1. Turn the ignition OFF for 10 seconds.
2. Connect the scan tool to the data link connector.
3. Turn the ignition ON with the engine OFF.
4. Use the scan tool in order to retrieve history DTCs from all modules.
5. Clear all history DTCs.

BCM Functions

The Body Control Module (BCM) performs multiple body control functions. The BCM can control devices directly connected to its outputs based on input information. The BCM evaluates this information and controls certain body control systems by commanding outputs on or off. The BCM control inputs can be

1. Sensors and switches that are directly connected to the BCM
2. Class 2 serial data received from other vehicle systems connected to the class 2 serial data link.

The BCM is also capable of controlling other vehicle systems that are not directly wired to the BCM. The BCM does this by sending specific messages on the class 2 serial data link. The system capable of performing the required function will respond to the BCM message.

The BCM controls these functions

1. Audible warnings, refer to «AUDIBLE WARNINGS DESCRIPTION AND OPERATION (AUDIBLE WARNINGS)»(/buick/century/vi-1997-2005/remont/gauges-instrument-panels/#instrument-panel-gages-and-console__audible-warnings-description-and-operation-audible) in Instrument Panel, Gages and Console
2. Automatic door locks, refer to «POWER DOOR LOCKS DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/door-locks-anti-theft-systems/#door-system-mirror-system-window-system) in Doors
3. Automatic headlamp control, refer to «EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/exterior-lights/#lighting-systems) in Lighting Systems
4. Interior lighting, refer to «INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPE»(/buick/century/vi-1997-2005/remont/exterior-lights/#lighting-systems) in Lighting Systems
5. Keyless entry (AUO option), refer to «KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/door-locks-anti-theft-systems/#keyless-entry-system) in Keyless Entry
6. Passlock theft deterrent, refer to «VEHICLE THEFT DETERRENT (VTD) DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/door-locks-anti-theft-systems/#theft-deterrent-system__vehicle-theft-deterrent-vtd-description-and) in Theft Deterrent
7. Retained Accessory Power (RAP), refer to «RETAINED ACCESSORY POWER (RAP) DESCRIPTION AND OPERATION»(/buick/century/vi-1997-2005/remont/accessories-control-systems/#retained-accessory-power) in Retained Accessory Power

Simple Power Mode Example

The power mode signal may be as simple as a B+ input wired to a particular ignition switch contact. If this is also the B+ supply to the module/device, the module/device will only operate with the ignition contact closed to B+. An example of this is the starter relay when it is wired directly to the CRANK/START contact of the ignition switch. When the CRANK/START contacts are closed, the starter relay is energized and provides a current source to the starter and starter solenoid. When the ignition switch leaves the CRANK/START position, the switch contacts open and the starter relay is de-energized. This removes the current source from the starter and solenoid and the starter operation stops.

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 Body Control Module (BCM). The BCM receives 4 signals/circuits from the ignition switch. These are the Ignition 0, Ignition 1, Crank and Accessory 1 ignition switch signals/circuits.

To determine the correct power mode the BCM uses

1. The state of these signals/circuits, either switch closed (B+ = 1) or switch open (open = 0)
2. The sequence of switch closures received by the BCM
3. The status of the engine run flag.

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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 BCM fail to send a power mode message. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power mode.

Serial Data Messages

The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid BCM message until they can check for the engine run flag status on the serial data circuits. If the BCM 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 BCM 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, B+, 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.

See also:
• BATTERY NEGATIVE CABLE DISCONNECT/CONNECT PROCEDURE
• CLOSEOUT/INSULATOR PANEL REPLACEMENT -- LEFT
• PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS
• AUDIBLE WARNINGS DESCRIPTION AND OPERATION (AUDIBLE WARNINGS)
• POWER DOOR LOCKS DESCRIPTION AND OPERATION
• EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION
• KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION
• VEHICLE THEFT DETERRENT (VTD) DESCRIPTION AND OPERATION
• RETAINED ACCESSORY POWER (RAP) DESCRIPTION AND OPERATION
• BODY CONTROL SYSTEM DESCRIPTION AND OPERATION
• BODY CONTROL MODULE (BCM) PROGRAMMING/RPO CONFIGURATION