2018 GMC Sierra 1500

*A message and alarm kept going off on our truck "Service Trailer Brake". We are not towing a trailer, nor had we had a trailer hooked to this vehicle since 2019. It began only going off occasionally, but within a few weeks it was going off constantly. It would show repeatedly on the dash and the alarm would sound over and over. Trying to turn off the system was not successful, no matter how many times we hit dismiss. It was totally distracting and worrisome that something was wrong with our braking system in general. *The constant alarm and dash display made driving a very distracted experience. It is so loud that you cannot hear other outside noises. We were also concerned about the safety of our regular braking system. *I called the dealer where our truck is regularly serviced. They immediately said "Is it the Trailer Assist Alarm?," so it was obvious that this is happening to other owners regularly. It took several days to get in for an appointment. The shop mgr helped us to locate and pull the alarm fuse to stop the noise, so we could drive it to the dealership later in the week. The display was still going off when I pulled the truck into the dealership, as it has done all the way there (17miles from my home). *It was inspected by the GM dealership (Schwarz, INC. Honesdale, PA) and the defective switch was replaced at a cost to us of $127.14 on 08/11/2022. *This issue started several months ago (Feb 2022?), but it was a one time thing. So, we thought it was just a fluke. Then, a month or so ago it started again, but was happening only once or twice and would then disappear for days. Then, 2 weeks ago it began to happen continuously.

Trailer brake modulator on 2018 GMC Sierra does not consistently signal trail brakes to work when needed on our 7,500 pound RV trailer. GMC dealer eventually found that the battery cables were undersized as installed with the factory towing package on the 2018 GMC Sierra. The undersized battery cables do not consistently deliver adequate voltage to the trailer brake modulator on the GMC Sierra, so inconsistent electric brake function for our 7,500 pound RV trailer. Dealer had difficulty diagnosing the problem as being the wrong factory-installed battery cables to go with the factory-installed trailer towing package. So it cost us $1,600 to have the GMC dealer correct a problem caused by the GMC factory installing undersized battery cables. Fortunately, this did not result in a collision for us, but it might for someone else. Our 2018 GMC Sierra kept sending vague, randomly timed warnings to the dashboard to "Check Trailer Wiring." Very frightening, dangerous and costly (for us) mistake by GMC. Will the brakes work this time, or fail on the way home? Problem started in 2021 RV season, but took awhile for us to recognize the need to take to the GMC dealer for them to diagnose base cause. Took time for us to experiment changing trailer wiring connector on bumper and trailer brake control on the dash. Work for awhile, then fail. Work for awhile, then fail. Arrrrgh! Ask GMC to put more adequate battery cables on ALL their vehicles, please.

While driving parking lot speeds, when I pressed the brake pedal, it was very very difficult to push causing me to nearly rear end the car in front of me. This happened intermittently during a short time frame (5 minutes). While standing on the brake pedal hoping to stop in time, the brake pedal shook like the Antilock brakes were activating. This caused it to be even more difficult to stop in time. My vehicle is currently at my local dealership's service shop. When the issue occurred, a message stating "Service Brake Assist" popped up in my display.

At 50,000 miles the "service trailer brake system" error message appears constantly due to factory defects and its very common. These trucks should be recalled everyone is in danger on the roads and its a very common problem. I have not taken it to the dealer because i should not have to pay for this very common problem, it should be recalled.