Moderator: (Still learning what the appropriate place is to post certain questions, so you may move this to wherever it should be.)
Just took delivery on a 2016 GMC Sierra 3500HD DRW Denali. I pulled my 40' Salem Hemisphere for several months last year with my 2014 (same model truck) and didn't even know it had a brake controller. I just "ASSumed" that it was automatic. So, now I am trying to figure out the proper procedure to adjust the "Trailer Gain".
The truck dealer has no clue. The trailer dealer has no idea what I am talking about, so now I am into the truck manual and I almost busted a gut when I encountered the following verbiage on page 244 of the 2016 GMC Sierra Denali manual.
1. Drive the vehicle with the trailer attached on a level road surface representative of the towing condition and free of traffic at about 20 t0 25 MPH and fully apply the Manual Trailer Brake Apply Lever.
Adjusting the Trailer Gain at speeds lower than 20 to 25 MPH may result in an incorrect gain setting.
2. Adjust the Trailer Gain, using the Trailer Gain Adjustment Buttons, to just below the point of trailer wheel lock-up, indicated by the TRAILER SQUEAL OR TIRE SMOKE WHEN A TRAILER WHEEL LOCKS.
There's more regarding what to do if your overloaded etc, but this was enough to make me sit up and take notice.
I see that the Trailer Brake Apply Lever is spring loaded so that answered my question about where you leave it after the exercise. I also understand that the Trailer Brake Apply Level controls ONLY the trailer brakes and not the truck brakes.
I am left with a picture of me squeezing the Manual Trailer Brake Apply Lever until it stops with my thumb and index finger of my left hand, and using my left pinky to cycle through the 1,000 possible Trailer Gain settings (0.00 to 10.00), while driving the vehicle with my right hand, and my wife hanging her head out of the window listening for tires squealing and watching for smoke. Then, backing the gain back down until the noise and smoke stops. AND, you're suppose to go through this exercise anytime the trailer load or road conditions change.
I'm sorry. but the way I see it, either I am reading the instructions incorrectly, they are written by a complete idiot, or the latest technology GMC has to offer (in their most expensive truck) is not much better than trailer towing technology back in the 1940s. Surely, something is wrong here.
I would be very appreciative to hear from anyone that has done this is a GMC truck and tell me how they did it.