Service trailer brake system

QuadRacer041

Senior Member
Location
northern nj
Been having this issue with my 09 3500hd for a while now. I have replaced the brake controller relay along the frame rail and the fuse in the engine compartment a few times. It would fix the problem for a little while then it would start to happen again. Now a new one doesn't do anything. I have checked resistance from the trailer plug to the ground wire under the drivers door which im pretty sure is the trailer controller ground and there is no resistance. I have removed the wire loom from most of the harness in the back section of the truck and do not see any issues. When I probe the back of the trailer brake with in the cab while manually engaging the slider I do go from zero voltage to around 5 volts on 2 wires I believe. then there are another 2 wires that have voltage and when I engage the slider they go to zero volts. So I think the switch is working. I do have power getting to both the relay and module along the frame rail. The blue wire from the relay to the trailer connector does have continuity. But I don't know what wires from the cab to the module or relays I should text for voltage. Anyone have any ideas or resolutions????? Im stumped!
 

SilverPine

Senior Member
Theres a relay/module near the spare tire. I replaced it twice in 4 years. I started getting the message again right before winter. They get covered in salt, not a great design. I leave my spare tire off so it gets covered in dirt and salt year round.

Edit: I also replaced the factory controller. The whole trailer brake system in that model is very unreliable.
 

boutch

Senior Member
Location
Nova Scotia
I was trouble shooting a brake controller on a 2013 truck. I was puzzle like you. My voltage probing the plug in the bumper were all messed up. It turn out with the integrated brake controller it doesnt send power to plug if it doesn't see a trailer plugged in. I thought the truck was the problem but turned out was the break away battery charger was shorted on the trailer.
 

SilverPine

Senior Member
From the dealer. He said plug and play. Installed it myself and it didnt work. Brought it back in and the tech said "that happens sometimes with these electronics". $120 reprogram fee later, worked great.
 

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