Body Control System Chevrolet Avalanche I

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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

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.

Ignition Accessory: Input from ignition switch Accessory circuit. Used to determine power mode. Hot in ACC and ON.

Ignition 0: Input to the control module from the ignition switch indicating the Ignition 0 position. Switch closed (HOT) in ignition switch positions UNLOCK, ACC, ON, and START

Ignition 1: Input to the control module from the ignition switch indicating the Ignition 1 position. Switch closed (HOT) in ignition switch positions ON and START

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

Julian Date of Build: The day of the year when module was built.

Seed and Key Timer: Indicates the time remaining for programming functions.

Year Module Built: The year when module was built.

8 Digit GM Part Number: The module's part number.

Scheme 46

Circuit Description

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

Conditions for Running the DTC

The module 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

The module has detected an internal malfunction.

Action Taken When the DTC Sets

The module 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.

Diagnostic Aids

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.

Scheme 47

After entering RUN mode, the inflatable restraint sensing and diagnostic module (SDM) and Radio receive the VIN from the BCM, via the class 2 serial data circuit. The SDM also receives a message from the BCM containing its restraints ID. The restraints ID contains the last four digits of the SDM part number. The modules compare the information stored in their memory with the information received from the BCM.

Battery voltage is between 9-16 volts.

The restraints ID that is stored in the SDM does not match the restraints ID that is stored in the BCM or the VIN information that is stored in either the SDM or Radio does not match the VIN information that is stored in the BCM.

The following module specific actions may occur

1. The SDM commands the AIR BAG indicator ON via a class 2 serial data message.
2. The SDM disables all deployment loops.
3. The radio does not function and displays as many characters of the word "CALIBRATE" as will fit on the display.

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.

DTC B1001 is an indication that the restraints ID stored in both the BCM and the SDM do not match or that the VIN stored in the BCM does not match the VIN stored either in the SDM or in the radio. If any of the modules mentioned above were previously replaced, the replaced module needs to be reprogrammed for proper operation.

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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.

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.

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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.

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.

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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.

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.

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The body control module (BCM) is the power mode master responsible for sending ignition switch position information on the class 2 serial data link. The BCM monitors 3 discrete wires from the ignition switch contacts and the engine run flag (ERF) in order to determine the present power mode. The BCM communicates this power mode information to all class 2 modules on the class 2 serial data link. The following table represents correct BCM power mode data

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The only requirements are voltage and ground.

One of the 3 monitored ignition switch circuits has malfunctioned. The DTC will set, if one of the following situations is present

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The BCM implements default actions for each ignition switch position when faults are detected.

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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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 TCS indicator turns ON.
4. The EBCM disables the ABS/DRP/TCS.

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.

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.
3. If this DTC continues to set intermittently, replace the module

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Important: Review the system operation in order to familiarize yourself with the system functions. Refer to BODY CONTROL SYSTEM DESCRIPTION AND OPERATION .

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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Removal Procedure

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1. Disconnect the negative battery cable(s).
2. Remove the knee bolster. Refer to KNEE BOLSTER REPLACEMENT in Instrument Panel, Gages, and Console.
3. Disconnect the brown connector.
4. Disconnect all other connectors (1).
5. Remove the BCM from the sliding bracket.

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1. Slide the BCM onto the bracket.
2. Connect all the connectors (1) except the brown connector.
3. Connect the brown connector.
4. Install the knee bolster. Refer to KNEE BOLSTER REPLACEMENT in Instrument Panel, Gages, and Console.
5. Connect the negative battery cable(s).
6. Reprogram the BCM. Refer to «BODY CONTROL MODULE (BCM) PROGRAMMING/RPO CONFIGURATION»(/chevrolet/avalanche/i-2001-2006/remont/communication-devices/#body-control-system) .
7. Perform the Passlock Learn Procedure. Refer to PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS in Theft Deterrent

Introduction

The procedures below are designed to set-up the body control module (BCM) correctly during BCM related service. Before you start, read these procedures 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. Perform the PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS in Theft Deterrent after successfully finishing the Setup New BCM procedure. If the PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS in the Theft Deterrent 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 system. The engine will not crank nor start.

Setup New Body Control Module (BCM)

Refer to SERVICE PROGRAMMING SYSTEM REMOTE PROCEDURE or SERVICE PROGRAMMING SYSTEM PASS-THRU PROCEDURE or SERVICE PROGRAMMING SYSTEM OFF BOARD REMOTE PROCEDURE) or SERVICE PROGRAMMING SYSTEM OFF BOARD PASS-THRU PROCEDURE in Programming.

Important: After programming, perform the following to avoid future misdiagnosis

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 control modules 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 control module 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 in Instrument Panel, Gages and Console
2. Automatic door locks, Refer to POWER DOOR LOCKS DESCRIPTION AND OPERATION in Doors
3. Automatic headlamp control, Refer to EXTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION in Lighting Systems
4. Interior lighting, Refer to INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION in Lighting Systems
5. Keyless entry (AUO option), Refer to KEYLESS ENTRY SYSTEM DESCRIPTION AND OPERATION in Keyless Entry.
6. Passlock theft deterrent, Refer to VEHICLE THEFT DETERRENT (VTD) DESCRIPTION AND OPERATION in Theft Deterrent.
7. Retained Accessory Power (RAP), Refer to RETAINED ACCESSORY POWER (RAP) DESCRIPTION AND OPERATION in Retained Accessory Power

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 uses 3 signals from the ignition switch. These are the Ignition 0, Ignition 1, and Accessory.

To determine the correct power mode the BCM uses

1. The state of these signals
2. The sequence of switch closures received by the BCM
3. The status of the engine run flag

The chart indicates the power modes detected and transmitted by the BCM

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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 receive the engine status from the PCM. 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 DISCONNECT CAUTION
• BODY CONTROL SYSTEM DESCRIPTION AND OPERATION