Towing

[Jeff20]

I purchased a 2020 GMC terrain. When I tow a trailer, my brakes lock up when I shift into reverse. I am able to tow moving forward with no problems but as soon as I shift into reverse, the brakes on the vehicle lock up almost as if I’m stepping on the gas pedal and the brake pedal at the same time. This obviously makes it impossible to back up while towing a trailer.

[Doug_Scott]

I think you will find your trailer brakes are coming on.  Some trailers have a brake system in the tongue of the trailer that is activated by the trailer moving forward on the hitch, causing the master cylinder (if hydraulic brakes on trailer) in the tongue of the trailer to apply the trailer brakes.  Those trailers typically have a lock-out pin you insert to back up.  Think of the receiver that the ball goes into as being a brake pedal.  When the truck slows, the trailer brakes will be applied by the receiver moving forward on the ball, applying the brakes.  They cannot be applied too much because the receiver would move backwards releasing the trailer brakes.  Pretty ingenious system, except for backing up.  The lock out pin stops the receiver from moving.  I think.  Been far too long since I last saw one.