Fix Your Truck’s Electrical Gremlins for Good
Is your GMC Sierra or Chevy Silverado experiencing a frustrating array of electrical issues? One moment the A/C works, the next it doesn’t. The power locks have a mind of their own, and a persistent airbag light stays on your dash. These aren’t separate problems; they’re classic signs of a failing Body Control Module (BCM). As the electronic nerve center for your truck’s comfort and convenience features, a faulty BCM can cause chaos. This replacement BCM, part number 20939138, is the reliable, straightforward solution. We pre-program it to your truck’s specific VIN, so it arrives ready for a quick, plug-and-play installation, getting you back on the road without a costly trip to the dealership.
Is Your GM Truck Showing These Telltale Signs?
- ✔ The HVAC system or blower motor works intermittently or not at all.
- ✔ An airbag warning light is illuminated, often with a diagnostic trouble code (DTC) like B1001.
- ✔ Power windows, door locks, or interior/exterior lights are behaving erratically or have stopped working.
- ✔ The security system malfunctions, leading to no-start conditions, stalling, or misfires as the anti-theft system engages incorrectly.
- ✔ Your scanner is pulling multiple communication or body-related trouble codes.
A Technician’s Notebook: The Case of the Phantom Ground
A customer brought in a 2009 Silverado 2500 with a textbook case of BCM failure—flickering dash lights, radio cutting out, the works. He had already replaced the BCM himself, but the problems returned within a week. My first step wasn’t the module, but the ground points. On these GMT900 platforms, the primary BCM ground is located on the A-pillar near the driver’s left foot. Sure enough, it was corroded from years of winter salt and moisture. After cleaning the contact point to bare metal and re-securing the ground, we installed one of our pre-programmed BCMs. The truck has been running without a single electrical glitch for over a year. Lesson learned: A new part can’t fix a bad connection. Always check your grounds during a BCM replacement to ensure a permanent repair.
A Straightforward Guide to Installation
Replacing the BCM in your truck is one of the easier electrical jobs you can tackle. You can have the new module in and running in less than 15 minutes.
- Safety First: Always disconnect the negative terminal from your vehicle’s battery before working on any electronic components.
- Locate the BCM: On most GM trucks and SUVs from this era, the BCM is located under the driver’s side of the dashboard, usually to the left of the steering column.
- Remove Connectors: Carefully unplug the multiple wiring harness connectors from the old BCM. They have locking tabs, so be gentle to avoid breaking them.
- Swap the Module: Unclip or unbolt the old BCM from its mounting bracket and set it aside. Snap the new, VIN-programmed module into place.
- Reconnect and Test: Plug all wiring harnesses firmly into the new BCM. Reconnect your battery terminal. Start the vehicle and test all functions: lights, wipers, locks, windows, and HVAC to confirm the repair.
Post-Installation Note: In some cases, an airbag light may remain on. This requires a professional scan tool to perform the “Setup SDM Primary Key in BCM” function to sync the modules. Additionally, a Brake Pedal Position relearn may be needed. These procedures are only necessary if related warning lights or issues are present after installation.
Verified Vehicle Compatibility
This module is a direct replacement for part number 20939138 and other interchangeable numbers on a wide range of General Motors vehicles. Please confirm your model and year below.
ESCALADE & ESV & EXT 07-11
SIERRA 1500 PICKUP 07-11
SIERRA 2500 PICKUP 07-11
SIERRA 3500 PICKUP 07-11
SIERRA DENALI 1500/2500/3500 07-13
SILVERADO 1500 PICKUP 07-11
SILVERADO 2500 PICKUP 07-11
SILVERADO 3500 PICKUP 07-11
SUBURBAN 1500/2500 07-11
TAHOE 07-11
YUKON & YUKON XL 1500/2500 07-11
This part also interchanges with: 25835966, 15263363, 15263497, 15878753, 15284816, 15943678, 15926094, 15940214, 25790508, 25790509, 25823558, 25823559, 25835965, 25844479, 25971916, 25971917, 15901388, 20939137, 22860591.
Frequently Asked Questions
What does “VIN Programmed” mean for me?
It means this Body Control Module will arrive at your door ready to install. We load your vehicle’s specific VIN onto the module before shipping, ensuring it communicates perfectly with your truck’s other systems right out of the box. This lets you skip the expensive and time-consuming programming appointment at a dealership.
Do I need to return my old BCM? Is there a core charge?
No. We do not require you to send back your old part. There is absolutely no core charge, making the transaction simple and hassle-free.
Why is my airbag light still on after installation?
For safety, the BCM and the Sensing and Diagnostic Module (SDM, or airbag module) are linked. If the light persists, it means they need to be re-synced. A professional mechanic can do this with an advanced scan tool using the ‘Setup SDM Primary Key in BCM’ function. This is a quick procedure that resolves the light.
Will this fix my air conditioning and heater problems?
Yes, in many cases. The BCM directly controls the HVAC head unit and the blower motor relay. If your climate controls are acting erratically or the fan only works on some speeds, a failing BCM is a very common cause.
Is this a difficult part for a DIY mechanic to install?
Not at all. This is considered a very DIY-friendly repair. With basic hand tools, you can typically locate and swap the BCM in under 15 minutes. It’s usually held in place by simple clips or a few small bolts under the driver’s side dashboard.