Seeing the dreaded ‘Service Trailer Brake System’ message on your dash? As a mechanic with over two decades of experience, I know how frustrating—and dangerous—that warning can be. When you’re hauling a heavy load, you need absolute confidence in your braking system. This genuine GM Trailer Brake Control Module (TBCM) is the definitive solution for your 2013-2014 GM HD truck or SUV, restoring both function and peace of mind.
The TBCM is the brain behind your truck’s integrated trailer braking system. It communicates with your vehicle’s main computers to apply the trailer’s brakes proportionally to your truck’s braking effort. Unfortunately, due to its mounting location on the vehicle’s frame, it’s highly susceptible to corrosion from road salt, water, and debris. This exposure is the number one cause of failure I’ve seen in my shop, leading to communication errors and a complete loss of trailer brake function.
We take the guesswork and dealer expense out of the repair. Simply provide us with your vehicle’s VIN after purchase, and we will program this module with the very latest GM software specific to your truck. It arrives at your door ready for a simple, direct-fit installation. No expensive trips to the dealership for programming are required. This is the most efficient way to get your 2013-2014 Silverado TBCM system working like new again.
Is Your Truck Displaying These Warning Signs?
- ✔ ‘Service Trailer Brake System’ message on the Driver Information Center (DIC).
- ✔ Trailer brakes not engaging or engaging erratically.
- ✔ Inability to adjust trailer gain settings on the dash controller.
- ✔ Diagnostic Trouble Codes (DTCs) stored, such as C1512, C1523, or U0100 (Lost Communication With ECM/PCM).
- ✔ The trailer disconnects and reconnects randomly while driving.
From the Diagnostic Bay
A customer brought in his ’14 Sierra 3500, convinced he needed a new in-dash brake controller switch. His trailer brakes were completely dead. He’d already spent money on a new 7-pin connector with no luck. After a quick scan, I saw a ‘Lost Communication’ code with the TBCM. I bypassed the fancy interior parts and went straight to the module on the driver-side frame rail. It was caked in mud and the connectors were green with corrosion. We installed one of these pre-programmed modules, and in 15 minutes, his system was fully operational. It’s a classic case of the problem being at the source, not the switch.
A Straightforward Guide to Replacing Your TBCM
Replacing your 2013-2014 Silverado TBCM is a job most DIYers can handle with basic tools. This module is typically found on the driver’s side frame rail.
- Safety First: Always disconnect the negative terminal from your truck’s battery before starting any electrical work.
- Locate the Module: On most pickups, find the TBCM mounted to the inside of the driver-side frame rail, roughly between the cab and the rear axle. On Suburbans and Yukons, it’s often on the LH middle of the frame.
- Disconnect Electrical Connectors: Carefully press the release tabs and pull the two electrical connectors straight out. Inspect them for any corrosion or damage.
- Remove Mounting Bolts: Use a socket wrench to remove the bolts securing the module to the frame bracket.
- Install the New Module: Mount your new, pre-programmed TBCM onto the bracket and tighten the bolts. A small amount of dielectric grease on the connector pins is a great pro-tip for preventing future corrosion.
- Reconnect and Test: Plug the electrical connectors in firmly until they click. Reconnect your battery, start the truck, and verify the ‘Service Trailer Brake System’ message is gone.
Verified Fitment for Your GM Truck or SUV
This module, part number 20964299 (also replaces 20850923), is a direct-fit replacement for the following vehicles equipped with the towing control option. Your VIN is used to ensure perfect software compatibility for your specific 2013-2014 Silverado TBCM and other listed models.
- ✔ 2013-2014 Chevrolet Silverado 2500 / 3500 Pickup
- ✔ 2013-2014 GMC Sierra 2500 / 3500 Pickup
- ✔ 2013-2014 GMC Sierra Denali 2500 / 3500
- ✔ 2013 Chevrolet Suburban 2500
- ✔ 2013 GMC Yukon XL 2500
Frequently Asked Questions
Why do I need to provide my VIN?
Your VIN (Vehicle Identification Number) allows us to load the exact, correct software from GM for your truck’s specific options. This ensures the module communicates perfectly with your other vehicle systems, making it a true plug-and-play part.
Is this part difficult to install?
No, this is a very straightforward installation for someone with basic mechanical skills. It involves unplugging the old module and bolting the new one in its place on the frame rail. No special tools are required.
What is the difference between this and the controller in the dash?
The controller in your dash is just the user interface—the switch and gain adjustment slider. This TBCM is the actual computer, mounted on the frame, that does all the work of interpreting signals and applying the trailer’s brakes.
Will this fix the ‘Service Trailer Brake System’ error?
In the vast majority of cases, yes. A failed TBCM is the most common cause of this warning message on these GM trucks. This pre-programmed module is the direct solution for a faulty original part.
Are part numbers 20964299 and 20850923 interchangeable?
Yes, part number 20964299 is the correct and updated replacement for the older 20850923 module. It is fully compatible with all vehicles listed.