Body Control System: Other Chevrolet Silverado 2500

Intermittent

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

Body Control Module (BCM) Programming/RPO Configuration

Important: If the module is replaced, programming the module with the proper RPO configurations must be done prior to performing the Passlock Learn procedure.

1. The BCM must be programmed with the proper RPO configurations. The BCM stores the information regarding the vehicle options. If the BCM is not properly configured with the correct RPO codes the BCM will not control the features properly. Ensure that the following conditions exist in order to prepare for BCM programming: The battery is fully charged. The ignition switch is in the RUN position. The DLC is accessible. All disconnected modules and devices are reconnected before programming.
2. Follow the SPS instructions on the Techline Terminal and scan tool to program the BCM.
3. If the BCM fails to accept the program, perform the following steps: Inspect all BCM connections. Verify that the SPS Techline Terminal and scan tool have the latest software version.

Passlock Learn Procedures

Refer to PROGRAMMING THEFT DETERRENT SYSTEM COMPONENTS for the appropriate learn procedure.

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 it 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 & OPERATION»(ref-176702-S32042800312005051000000) .
2. Automatic door locks, refer to «POWER DOOR LOCKS DESCRIPTION & OPERATION»(ref-176715-S26038349742005051100000) .
3. Automatic headlamp control, refer to «EXTERIOR LIGHTING SYSTEMS DESCRIPTION & OPERATION»(ref-176693-S09398546132005051000000) .
4. Interior lighting, refer to «INTERIOR LIGHTING SYSTEMS DESCRIPTION & OPERATION»(ref-176693-S16923395092005051000000) .
5. Keyless entry (AUO option), refer to «KEYLESS ENTRY SYSTEM DESCRIPTION & OPERATION»(ref-176703-S15043449712005051200000) .
6. Passlock theft deterrent, refer to «THEFT SYSTEMS DESCRIPTION & OPERATION»(ref-176706-S32879241292005051200000) .
7. Retained Accessory Power (RAP), refer to «RETAINED ACCESSORY POWER (RAP) DESCRIPTION & OPERATION»(ref-176709-S31264998322005051200000) .

Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMN). On this vehicle the PMM is the Body Control Module (BCM). The BCM receives 2 signals/circuits from the ignition switch. These are the Ignition 1 and Ignition 3 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 = O)
2. The status of the engine run flag.

The chart indicates the modes detected and transmitted by the BCM. see scheme 20

Scheme 14

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.