I just bought a new 2021 F150 i had a 2018. the new 1 has backup assist and im not going to set it up since i can back a trailer just fine. My question is i was backing my boat in the drive today and the damn thing basically slammed on the brakes as i was backing from the road to the drive. Why did it do that and how do I make it stop doing that

 

You mentioned boat trailer. Most boat trailers have a surge brake for braking. So backing up slid the slide just enough to engage the brakes. Common on boat trailers and on 6x12 uhaul trailers.

 

It does have surge brakes but when i pulled it with my 2018 f150 i never had the problem. Its just odd the 1st time i pulled it with the new truck i had an issue

 

Mine has done goofy things. Older it gets, better it gets. If you were in tow mode, it might have thought the boat was pushing the truck and reacted.

 

Others with this issue have been told to go into settings and turn off "reverse brake assist."

 

Probably the backup sensors automatically putting the brakes on when it "saw" the boat. Was there any alerts / warnings? If so, follow Darklock's advice.

 

Before I read the post about the reverse brake assist I discovered the reverse brake assist and turned it off. Thanks everyone for the help

 

I towed my 21' travel trailer with my new 2021 King Ranch for the first time and everything works fine, but after 20 minutes of driving the "Trailer Not Connected" message appears. Has anyone else had this happen? All equipment is new so I think it must be a TBC or computer problem(??) Brakes, lights, everything still works even with the message displayed.