No trailer brakes after tripping & resetting breakaway switch-- Fixed and a warning!

JimPetzold · July 2, 2022

Last week, I tripped my breakaway switch and locked up the trailer brakes when I made a tight turn & the cable hung up. I reset the switch & the brakes released but now I have no trailer brakes & I get the service trailer brake system error. Anyone have an idea?

Warning, I read about a guy that had a DOT/DMV check pull the switch to test the system. It blew his electronic controller. Be sure to un-hook the trailer plug from the truck before letting them test the system.

Edited July 10, 2022 by JimPetzold

asilverblazer · July 5, 2022

Check the fuse, pulling the plug out sends full voltage to the brakes, might have pulled too many amps and blew the fuse.

JimPetzold · July 10, 2022

ok, I studied the system. when the trailer brakes are actuated by the breakaway switch, the power comes from the on-board trailer batteries (group 27 rv type battery). It apparently back fed the power surge into the controller above the spare tire & fried that. ended up changing that and both 30 amp fuses, for the brake feed & the 12 from the truck to the trailer battery.

I purchased a Foxwell NT510 GM scanner and was able to read all the codes & could see the exact sequence of events that fried the controller, actually pretty interesting. After the controller was changed it still gave me a CCM code for lost communication & the fuse was the culprit. When I was on the road trying to fix it with nothing, I had swapped fuses with the trailer battery fuse and apparently that was blown too.

Great code scanner, I want to find resource to read more about how the onboard systems work, Guess that is just the nerd in me coming out!

Will make sure I have the tools & spare parts on hand before I head out on a road trip again.