Troubleshooting Brake Controller on 2008 GMC Sierra That Activates Without Applying Brake Pedal

Question:

I have a 2008 GMC Serria. i have had 2 different controllers, Reese and a Trkonsha. Both of these controllers activate with no yrailer hooked up and also while driving down roar the trailer brakes will active wothout pressing brake peddle, what can cause this. the factory ground is a 16 gague.

asked by: Harry D

Expert Reply:

Since the problem has occurred with two different brake controllers, I'd tend to rule out the controller being your problem.

I think I know what your problem is. 2000's era GM trucks were very well known for having faulty brake lamp switches. If both the controllers you've used are Time-Delayed brake controllers, a faulty brake switch would absolutely cause the problem you've been experiencing. There's a very easy way to test for this. With the ignition on, use a voltmeter or circuit tester like # PTW2993 on the red wire feeding the controller. Have a helper shake the brake pedal from side to side as rapidly as possible. If you see any voltage on that circuit, the brake switch is bad and needs replacement.

The other less likely possibility is a short in the brake output circuit on the trailer. You'll need to trace the brake output circuit from the trailer connector back to the magnets. Look for pinched or broken wires, loose connections, and cracked or worn wire insulation.

I'll link you to our trailer brake controller troubleshooting article which you might find helpful.

expert reply by: Mike L