Is Your GM Truck Plagued by Baffling Electrical Problems?
If your GMC Sierra, Chevrolet Silverado, or other GM truck is acting possessed—with flickering lights, unresponsive power windows, a dead HVAC system, or random warning lights—the culprit is often a failing Body Control Module (BCM). The BCM is the central command center for your vehicle’s body electronics, and when it malfunctions, it can cause a cascade of frustrating and seemingly unrelated issues. This genuine OEM-quality module, part number 20939137, is the definitive solution to restore order and functionality to your vehicle.
From the Diagnostic Bay
We had a 2009 Silverado 2500 in the shop that was driving its owner crazy. The radio would turn off randomly, the driver’s side power window worked only when it wanted to, and the anti-theft light would flash, sometimes preventing the truck from starting. The owner had already replaced the battery and checked fuses. After hooking up our scanner, we saw a handful of communication error codes pointing to the BCM. A quick check under the dash revealed a poor ground connection near the module, a common issue on these trucks. After cleaning the ground and installing this VIN-programmed BCM, every single electrical gremlin vanished. It’s a reminder that the BCM is the heart of the truck’s comfort and convenience systems.
Symptoms of a Failing BCM
- ✔ Unresponsive or erratic power windows, door locks, and interior/exterior lights.
- ✔ HVAC controls not working, or the blower motor functioning intermittently.
- ✔ The security system engaging randomly, causing no-start conditions or stalling.
- ✔ An illuminated airbag warning light, often with a DTC B1001 code stored.
- ✔ A dashboard that looks like a Christmas tree with multiple, unrelated warning lights.
- ✔ Communication errors with other modules when checked with a diagnostic scanner.
Why Choose Our Pre-Programmed Sierra 3500 Body Control Module?
This isn’t just a replacement part; it’s a complete, ready-to-install solution. We pre-program the module to your vehicle’s specific VIN, loading it with the latest GM software updates. This critical step ensures seamless communication with your truck’s other electronic systems, eliminating the need for an expensive trip to the dealership for programming. You get a BCM that is truly plug-and-play, designed to resolve common DTCs and restore your vehicle’s electronics to factory-perfect operation.
Key Features & Benefits
- ✔ VIN Programmed for You: Arrives ready for installation with no additional programming required.
- ✔ Restores Full Functionality: Corrects issues with lights, locks, windows, HVAC, and security systems.
- ✔ OEM-Standard Quality: Built to meet or exceed original equipment specifications for lasting reliability.
- ✔ No Core Charge: Keep your old part without the hassle or expense of a core return.
- ✔ Broad Compatibility: Interchangeable with numerous part numbers including 25844480, 25835966, 15943678, and more.
Installation & Post-Install Notes
Replacing your Sierra 3500 Body Control Module is a straightforward process. The BCM is typically located under the driver’s side dashboard, near the steering column. In most cases, the installation takes less than 15 minutes. However, be aware of potential post-installation procedures. If the airbag warning light remains on, a professional scan tool is needed to perform the ‘Setup SDM Primary Key in BCM’ function. Additionally, some models may require a ‘Brake Pedal Position Relearn’ to ensure proper brake light and traction control operation. Always consult a factory service manual for your specific vehicle if you are unsure.
Frequently Asked Questions
What does a Body Control Module (BCM) do?
The BCM acts as the central computer for your vehicle’s body electronics. It controls non-engine related functions like power windows, door locks, the security system, interior and exterior lighting, wipers, and the HVAC system.
Is this BCM really plug-and-play?
Yes. We pre-program the module to your vehicle’s VIN before shipping. This ensures it communicates correctly with your truck’s existing systems right out of the box, saving you a trip to the dealer for costly programming.
How do I know for sure my BCM is the problem?
While the symptoms listed are strong indicators, the best way to confirm a bad BCM is with a professional diagnostic scan. Look for communication error codes (U-codes) or specific BCM-related trouble codes (B-codes). Also, check for poor ground connections near the BCM, as this can mimic a module failure.
Where is the BCM located on my 2008 GMC Sierra?
On most 2007-2013 GM trucks and SUVs, including the GMC Sierra, the BCM is located under the driver’s side of the dashboard, often attached to a bracket near the steering column or junction block.
What if my airbag light is on after installation?
If the airbag light appears after you install the new BCM, it means the BCM and the Sensing and Diagnostic Module (SDM) need to be electronically synced. This requires a professional-grade scan tool to perform the ‘Setup SDM Primary Key in BCM’ procedure.