What Triggers "Check Trailer Wiring" DIC Message

Wxman · April 1, 2021

New truck, old trailer. First trip out everything flawless for the 3 hr trip to campground. A couple prior short test runs with setup had been flawless as well. On the return trip not so much. I probably received 35-40 "Check Trailer Wiring" messages on the DIC. These would be followed by a "Trailer Brakes Connected" message. Sometimes the connected message would be a second later, sometimes 30 sec or more later. During the time between the Check message and the Connected message I would have no trailer brakes, with pedal or with brake controller.

Trailer lights, the best I could tell, worked correctly at all times. If I called up the trailering app on the infotainment screen it always showed connections good, no faults detected. This was true even while the DIC was showing Check Trailer Wiring and I had no brakes.

My first question is what is the truck looking at when it triggers the "Check Trailer Wiring" message? I just need to know what the truck is checking and what parameters are "out" so I know where best to begin troubleshooting.

It went from perfect to scary and unreliable after three nights in the campground.

cfell · April 1, 2021

On our 2017 the brake circuit was not working properly. I tracked down several problems, including weak ground (cannot ground through the coupler only like in the old days). I ended up replacing the whip from the trailer to the truck and the other grounding issues, etc could diagnose.

cfell · April 1, 2021

Have someone sit in the truck while connected to trailer. Move each component around..if the DIC gives the trailer errors you are close to the problem(s)

Tomato · April 1, 2021

Sounds like it could be a loose 7-pin connection. I know the bumper receptacles like to have the trailer plug jammed in pretty tight...Pushed on harder than you would think necessary or good.

unit · April 2, 2021

I had the same problem after getting my 2020 Silverado. I swapped out the 7 way plug with a blade style plug after reading about the problem on another forum. The blade style plug makes better contact and feels more secure when attached to the truck. It's an easy swap and the blade style plugs are available everywhere RV parts are sold. You can see the differences in the two images below.

Non-Blade Plug

Blade Style Plug

Edited April 2, 2021 by unit

Wxman · April 2, 2021

Thanks for the replies. I knew I had to troubleshoot somewhere. I have traded plugs and entire umbilical cords with previous truck. I am running a Pollack blade style plug now. I eventually replaced one of the magnet assemblies when using old truck and everything seemed to be working. Got the new truck and started with 2.5 hrs of flawless towing and then couldn't keep brakes reliable.

I think I will check the grounds and maybe just completely rewire the brakes with some 12awg wire. At least I will know what I have with new wire.

CRApex · April 2, 2021

My guess is the ground. Also, I think the trailer might pick up a ground through the hitch. One of my trailers will work fine when its loaded with plenty of tongue weight but when most of the weight is on the rear of the trailer it triggers the message you've been getting.

skatville · April 4, 2021

I'm NOT 100% sure, but yesterday I added a plug to simulate that a trailer was connected to my 2020 GMC 2500HD Denali truck. I now get more camera views (side views) that are not available unless there is a trailer connected.

I added a 50 ohm resistor to the running lights and Right/Left/brake light terminals on the plug to the ground terminal. So on the plug I have 3 terminals with a 50 ohm resistor to ground. I then plug it in to the truck and started it up. Yep! A trailer was detected. I setup a new trailer profile, "Trailer Plug". Disabled the theft detection feature. The 50 ohm resistors where rated at 1 watt to be safe.

I determined the 50 ohm resistor by measuring the current from the trailer running lights when they were ON. About 1.1 amps. 14 VDC/ 1.1 A = 13 Ohms. To draw about 1/4 of that current, I increased the resistance to 50 Ohms. Then the power rating is about 14 VDC x (0.28A ^2) = 1 Watt.

With this all said- your problem could be an intermittent wiring issue on your trailer. Running light circuit or right/left/brake light circuits. Your electrical ground is routed thru the connector, so that could be intermittent as well.

Edited April 4, 2021 by skatville

Wxman · April 15, 2021

"Probably" found the problem. Picture is the wire I pulled out of the front trailer axle. On this trailer the brake wires run from the driver side wheel, through the hollow axle, to the passenger side wheel.

Intermittent problem. Had a terrible time finding issue until I just tore into everything to start replacing.

Another note of interest. I still don't know what the truck looks at or what actually trips the "Check Trailer Wiring" DIC message. On both trucks when I would get that message I would have no trailer brakes.

I discovered during troubleshooting that if one brake was completely disconnected I could still have brakes on 3 wheels, AND NOT GET ANY DIC MESSAGES. So, the lack of DIC messages does not mean everything is working. Gotta check those brake temps on heavy trailers and know that all the brakes are working, not just some of them.

Be safe everybody.

skatville · April 16, 2021

The truck (2020 2500HD Denali with towing package) checks the current on the running light circuit to detect a trailer. In my previous post above, I loaded the running lights and each brake light circuit with a 50 ohm ( 1 watt) resistor to the ground pin mounted in a trailer plug. I simply plug this in when the trailer is not connected to get the side camera to work. I disabled the theft deterrent feature, however, it is possible to use this feature as a trigger for an external alarm system.

Wxman · April 16, 2021

Yes, but I believe that is different than the "Check Trailer Wiring" message concerning brakes. The trailer app readout on the infotainment screen always knew when trailer was connected and showed no faults ever. I would get the "Check Trailer Wiring" message on the DIC, lose brakes, and the infotainment screen would still show connected, no faults (lights would work).

I have heard of many people having an issue with the truck knowing a trailer was connected or not. I haven't had that problem. The truck was detecting something specific to the brake system, which I believe I finally found. I am still just not sure what the truck is looking at to give that message and have brakes disabled. Based on the other indications I don't think it was the light load or wiring issue with lights. Also, my brakes have a dedicated ground all the way to plug. Nothing for brakes goes through frame or anything

Problem was with trailer though. I just thought if I knew what the truck was looking at it might make troubleshooting easier.

Thanks

Cheers.

Rider1122 · April 22, 2021

@wxman- you have this issue since? I’ve got a 2021 3500 and have the exact issue. Brakes will intermittently disconnect, running lights are all okay and towing app says all connections okay. One other interesting thing I’ve noted - when I get the brakes disconnected in dic my factory controller is dark (if u look when there’s symbol that lights up).

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Wxman · April 22, 2021

My symptoms were the same, including the little brake controller light. NO, I have not had the issue again after finding/fixing the shorted wire in the axle. Still don't know if issues other than a short can trigger those symptoms.

Good luck

Moconnor · May 16, 2021

I just got a new 2020 RST. First trip this weekend and this issue was driving me crazy. on the way home I started turning off stuff to see if it stopped the error. Well I have installed a rear camera on the factory Furion mount and added a passenger side camera also. they only work with the lights powered so I always drive with my light on on my other truck and so I was with this one as well. Turned off headlights and no error for miles. eventually turned them back on and error started right back up. when I got home I disconnect the side camera and what do you know, no more error. I have had this truck a week and first trip so I was frustrated to say the least. I just wanted to let yall know what worked for me.

Jon63ill · June 26, 2021

I’m also having problems with my new 12 foot enclosed trailer. My 2012 5th wheel works with my 2017 Denali 1500. Trying to set up a bench test with extra trailer coils. Next I’m going to do the resistors for lights to see if I can get the truck to notice a connection.