Weak Trailer Brakes Using P3 Brake Controller on 2012 GMC Sierra 1500 and 6K Trailer

Question:

I have a 2012 GMC Sierra 1500 towing an RV with a weight of 6000. Traveling at 25 mph and using the manual lever, I have to set the gain at 10 to stop the vehicle. Isnt that high?

asked by: Mike M

Expert Reply:

Not necessarily. A 6,000 pound trailer is going to have a lot of momentum and you have to consider that the 2012 GMC Sierra 1500 also has to be slowed by the trailer brakes when doing this test.

What I would do is make sure the brakes are adjusted out properly. You should here a slight but constant drag of the pads on the drum when the wheel is turned. Nine times out of ten issues with weak electric trailer brakes are the result of the brakes needing adjustment.

If you think that there is something else going on there are ways you can test a brake controller. In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # PTW2993 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override. If it shows power at idle then there is something wrong with the controller and it will need to be replaced.

If it tests fine then reconnect the blue wire. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.

You can test the brake output pin and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.

If the truck side checks out fine then it could be the wiring to the brake magnets or the magnets themselves. Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.