Instrument Cluster, Radio, Door Locks, and Windows quit working on my 2003 GMC Yukon XL SLT 4×4. Believe it to be in the BCM. Need schematics, Connector Charts, and Diagnostic connector Diagram to Help in Diagnosing. Thanks, Patches
Here is the information that I have including wiring diagrams. A blown fuse that is used by all systems described would be the first thing I would look for. And it would be the most common cause if they all went out at the same time. Since the vehicle is more than 10 years old, rusted ground connections may also be a factor.
Body Control System Description and Operation
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:
- Sensors and switches that are directly connected to the BCM
- 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:
- Audible warnings
- Automatic door locks
- Automatic headlamp control
- Interior lighting
- Keyless entry (AUO option)
- Passlock theft deterrent
- Retained Accessory Power (RAP)
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:
- The state of these signals
- Next , the sequence of switch closures received by the BCM
- Finally, the status of the engine run flag
The chart indicates the power modes detected and transmitted by the BCM:
Correct Ignition Switch Inputs
Ignition Key Position | Power Mode Parameter | Engine Running | Sampled Ignition Signal State | ||
|---|---|---|---|---|---|
Accessory | Ignition 1 | Ignition 0 | |||
| OFF | Off-Awake or RAP | No | Inactive | Off | Off |
| UNLOCK | Unlock or RAP Unlock | No | Inactive | Off | On |
| ACC | Accessory | No | Active | Off | On |
| ON | Run | No | Active | On | On |
| START | Crank | No | Inactive | On | On |
| ON | Run | Yes | Active | On | On |
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 MessagesThe 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 SignalsThose 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.
Body Control Module Programming
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.
Important
The following procedures must be followed:
- BCM Programming
- Programming Theft Deterrent System Components, if equipped with Passlock System.
Programming the BCM
Important
After the procedure is completed, the personalization settings of the BCM are set to a default setting. Inform the customer that the personalization must be set again.
Programming Theft Deterrent System Components
Important
This procedure has to be performed only for vehicles equipped with Passlock System.
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.
Important
After programming, perform the following to avoid future misdiagnosis:
- Turn the ignition OFF for 10 seconds.
- Connect the scan tool to the data link connector.
- Turn the ignition ON with the engine OFF.
- Use the scan tool in order to retrieve history DTCs from all modules.
- Clear all history DTCs.