Forum Discussion

CoMoCo's avatar
CoMoCo
Explorer
Aug 09, 2015

2015 GMC Sierra 3500 - Check Trailer Wiring

We just purchased a 2015 GMC Sierra DRW with the Duramax and integrated brake controller. I hooked up the trailer (a 2013 Lifestyle 36FW with the standard electric brakes) for the first time and I drove around my storage yard to set the gain on the brake controller. Then I went on the street for a longer test drive. During this test drive I started getting "check trailer wiring" popping up in the info centre followed a few seconds later by "trailer connected". I pulled into a parking lot thinking the trailer plug had popped loose but it wasn't loose. So I thought there was a loose wire from the installation of the in-bed plug that was installed using the factory 5th wheel wiring provision. I was using the in-bed plug that he installed. I did not try the factory plug at the bumper.

I stopped in at the installers on my way home from work the next day and he checked the wiring he did and everything was fine. He also checked the factory plug and it was fine as well. Both had proper voltages.

I don't believe there is anything wrong with my trailer plug as I never had issues like this with the old truck - a 2009 GMC Sierra DRW with the Duramax and integrated brake controller.

Does anyone have any ideas on what else I can look for? Would putting di-electric grease on the in-bed plug and the trailer plug help?

I plan to bring the truck and trailer to the installer when I have time so he can see both together.

Thanks in advance for any help.
Tow Vehicles
  • CoMoCo's avatar
    CoMoCo
    Explorer
    Aug 09, 2015
    The trailer plug fits fine in the truck receptacle - both the bumper and the in-bed plug. And I have the same issue with both. I will check the ground wire and then the trailer brakes - I am leaning towards either of these but am not ruling anything out.

    As far as I am aware the GM's only look for trailer brakes as well.

    Thanks for the tips!
  • deltabravo's avatar
    deltabravo
    Nomad
    Aug 09, 2015
    Some aftermarket receptacles and plugs on the trailer pigtail are made to very poor tolerances. Do the pair fit snugly or is there a lot of slop / wobble?

    One cargo trailer I use had a ****py tolerance plug on it and everytime I towed that trailer, the DIC would read "check trailer wiring"
    I finally got sick of the floppy plug and repalced the entire cord.

    Maybe the receptacle is the problem.... slightly over sized.
  • ib516's avatar
    ib516
    Explorer II
    Aug 09, 2015
    I had the same issue with my new Ram. No issue with the old truck snd aftermarket brake controller, but as soon as I hooked up the new truck I got the check trailer wiring message.

    I fiddled around with everything from cleaning contacts to changing the RV plug. Nothing worked. Finally took the RV into the dealer after trying a new rv on the lot with no problems. Turns out my rv had a faulty brake on one axle.
  • Farmerjon's avatar
    Farmerjon
    Explorer
    Aug 09, 2015
    I have had to clean the plugs for the same reason. On our ford the truck is only looking for the trailer brakes. When I have a trailer hooked up with out brakes on it the truck doesn't know I have a trailer hooked up, when I put it in reverse it warns me I'm to close.
    so you need to look at the ground and the brake wire and connections.
  • mooky_stinks's avatar
    mooky_stinks
    Explorer
    Aug 09, 2015
    I had this happen a couple weeks ago and it ended being the main ground wire on the trailer frame. I was getting "trailer connected" "trailer disconnected". Should be a white wire coming out of the trailer side harness. I grabbed it to see if it was loose and it fell off in my hand. I've towed since then and all is good. Something to check. I looked it up before I checked it and it's pretty common.
  • CoMoCo's avatar
    CoMoCo
    Explorer
    Aug 09, 2015
    The trailer plug worked without issue on my previous truck - a 2009 Sierra 3500 with the integrated controller so I thought it should be plug and play. All wires at both the factory bumper plug and the in-bed plug that the installer put in (using the factory wiring provision) had proper voltages when the were checked - I know - doesn't mean there can't be a loose connection somewhere.

    The message seems to appear when I take my foot off the brake pedal - not every time - but when it does appear it seems like I just took my foot off the brake.

    I will also get some electrical contact cleaner.

    Please provide suggestions if you have them for this problem.

    Thanks!
  • SouthpawHD's avatar
    SouthpawHD
    Explorer
    Aug 09, 2015
    I've noticed that sometimes the trailer plug doesn't stay seated very well in the TV. I have to push mine in extra hard to get it stay. Double check that you don't have any play in that connection.
  • The_Texan's avatar
    The_Texan
    Explorer
    Aug 09, 2015
    Sounds like you have a broken or loose connection in the factory harness. I would check at the back of the dash control and see how far I could trace the wiring.
  • donn0128's avatar
    donn0128
    Explorer II
    Aug 09, 2015
    Check the trailers plug. Get a can of electrical contact cleaner and spray liberally both sides.

About Travel Trailer Group

44,025 PostsLatest Activity: Feb 26, 2025