What Triggers "Check Trailer Wiring" DIC Message

[Phantom 4D]

I posted about this on another topic. Shortly after, I got some e mails from GM Executive Resolutions Team. The lady said they were contacted about my post, (GM lurking in the wings) I explained the issue word for word what was in my post. The lady contacted someone else in GM, quality team or some other group. Bottom line, She called back and said the issue was with the trailer, not the truck. Seems strange that I did a test two prior to the trip and had no problems at all. For the record, I was towing a 2013 20' enclosed trailer hauling two bikes. As was mentioned, the DIC message was constant in heavy rain, check trailer wiring, trailer brakes connected. And yes, the ITBC light would go on and off. Trailer lights worked without problem, even brake lights. I had the wiring on the trailer checked by an auto electrician and a trailer shop. They could not find a problem with the trailer. It seems strange that so many have had this same problem. By the way, my truck is a 2019 Sierra SLT X31. As soon as I get a dry day, I'm going to check everything myself. I did mention to the lady that I've been a mechanic for over 40 years. 

[THE YETI]

Had this issue in the past with 2 different 2015.5 Models. A GMC 2500HD 6.0L and a 2500HD High Country Duramax.  On either truck it happened only when either wet and raining.  Winter and snowing or slushy conditions or after a wash.  It WAS DEFINATELY the truck. After everything dried up it cured the problem. Even when I disconnected the trailer plug connections (at the bumper and the "T" I installed for the in bed plug) and put in dielectric grease it still didnt nothing to help.  I believe it was either a problem at another location of the wiring OR the connections have just enough play to leave a broken connection at times which would explain most of my issues being when it was cold when wiring would be much stiffer.  Just my experience.

 

Also. Only issue I've ever had with my 06'  LBZ Duramax is after so many years the butt connectors at the splices for my in bed plug corroded and needed attention. But that took 10 or 15 years of Canadian winters and the last few years of neglecting the car wash more often than before.

Edited June 30, 2021 by THE YETI

[kickass audio]

I had the check trailer wiring message come up on my DIC and I only once had a trailer connected to the 7 way connector on my truck and twice on the 4 pin connector. I noticed that the message just came up at random weeks after I last had a trailer on my 7 way connector. I did previously squeeze diaelectric grease in both connections to help prevent the problem of having any moisture get on the prongs and corrode them away.

 

I looked at the connector and noticed that the diaelectric grease I put in the connector was bridged between pins. What I did to stop my error was to use a tiny plastic zip-tie and remove the jumper of the diaelectric grease that was bridging the gap between the prongs on the connector in the bumper and my message went away immediately.

 

Again, my problem was random in that it came up 4 times with each restart of my truck with no trailer connected for over a month on my truck but it's worth mentioning to maybe help give another place to look at the problem.

[Erik Verfuss]

I had the same issue on a 2015.5 2500 Denali and they also told me that it was the trailers (2 of them), although both worked fine with other vehicles.  After several trips to the dealer, I mentioned it to my trailer dealer/hitch installer - he said that it the truck monitored amperage (actually milliamps) draw at the plug and that there must be an increased draw somewhere.  He cleaned the connections in the truck side of the plug - issue went away.  When it reappeared after a winter of snow and ice, he replaced the receptacle/plug in the bumper and the issue never returned...

[bharten]

I  have this EXACT same issue on my 2021 3500HD Duramax flatbed.  Bought the truck in June and hooked it up to a brand new tilt deck equipment trailer.  Everything was fine for a month or two, then the DIC starts chiming “Check Trailer Wiring/Trailer Brakes Connected”, randomly, but constantly.

Had the truck looked at, and the shop found two of the factory blades on the plug pushed in a bit, so they replaced the plug receptacle on the truck.  That did not fix the issue.

 

Dropped the trailer to a shop to look over the brand new trailer wiring, test the brake magnets, look at all the connections, and everything looked good.  Had them replace the plug on the trailer, in case there was something internal with it, and that didn’t fix it.

 

My 2021 truck will tow my older 2005 Featherlite enclosed trailer, with electric brakes, with zero issues, so that leaves the trailer suspect, right?  Not really.  When I tow the equipment trailer with my 2011 3500HD Duramax, it has zero issues with the trailer.  So which one is the issue?  Why do that specific truck and that specific trailer not play well together???

If I bring the trailer back to the dealership, they are going to tell me it is a truck problem, since everything checked out OK by the other shop.

I am ready to pull my hair out on this one.

[Kevin B]

I had the same issue on my 2021 3500 Denali first trip 600mi without any issues. Then, on the return trip the same symptoms occurred as happened to you guys - rewired the trailer first (since it is a 2006 model - naturally assumed it to be the problem, went with Curt 7 blade-style plug and 14awg light wires and 10awg brake wires) without any changes. Found a bent axle when rewiring the trailer, so I replaced both axles and brake assemblies - still had the issues. Finally convinced my local dealer that the issue was in the truck - they replaced the trailer brake module located under the spare tire, and I haven't had any issues since (Over 3000mi later)

[Sram]

On 4/4/2021 at 9:41 AM, skatville said:

"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." 

 

On 4/4/2021 at 9:41 AM, skatville said:

P=IV (Current x Voltage) = I^2 R (Current ^2 x Resistance) - you would need at least a 4 Watt rated resistor or risk burning the 1 Watt up.

 

[Sheila Wallendal]

Has anyone had the check trailer wiring warning when no trailer is attached?

 I’ve already replaced the bumper plug but still get the warning both with and without having anything attached.

[Plympat]

Follow-up 9/2/22 - repair shop found chaffed wire running through trailer axle (see photo), repaired, back in business.  I was fairly certain it was a truck problem - humbly admit it was in the trailer.  Similar to Wxman’s post last spring.  

Sorry to hear so many others with same issue as me, but then I'm glad I'm not alone...  Been chasing this same problem since last fall.  2020 GMC 3500HD Denali, 2017 Grand Design bumper pull travel trailer.  "Check trailer wiring" "electric trailer brakes disconnected" started at end of trip, after a month of travel and around 4000 miles with no problems.  Previously had pulled this same trailer for 3 years and 15k miles with 2017 GMC 1500, also with no issues.  Once home, GM dealer used trailer "simulator" plug to check truck, said no issues found, I should try replacing trailer plug with Pollack blade type plug.  Did that, same problem.  Took trailer to RV dealer, they checked trailer and said no issues found, must be truck.  Took truck back to GM dealer, had them replace bumper plug receptacle, same problem (but this did seem to solve intermittent video connection to GM OEM camera I installed on rear of trailer).  Latest effort to fix: dropped trailer at trailer maintenance shop nearby a few days ago.  They'll check out trailer wiring (as well as lubing bearings, and one tire not wearing evenly, maybe bent axle?)  I'm expecting the trailer wiring will check out fine (though originator of this post found melted wiring in his trailer axle, so maybe that??).  I also appreciate hearing Kevin B say earlier that his dealer replaced his truck's trailer brake module under the spare tire and that solved his problem.  Next idea...  Thanks to all for sharing.

 

Edited September 2, 2022 by Plympat
Update

[Plympat]

On 7/17/2022 at 11:26 AM, Sheila Wallendal said:

Has anyone had the check trailer wiring warning when no trailer is attached?

 I’ve already replaced the bumper plug but still get the warning both with and without having anything attached.

Have only had my problem when the trailer's connected.  Although, the truck's 30 amp "electric trailer brake" fuse has blown a few times, and that'll make the messages stay on even when the trailer's not connected.  

[maxfli11]

On 4/4/2021 at 10:41 AM, skatville said:

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.

So if i'm reading this right i need three 50ohm resitors in each circuit tied to ground for our LED lights.? Come on GM, you can do better. We have to jury rig out trailer wiring to adapt for engineering short commings.

[skatville]

Yes- 50 ohm resistors-  IMPORTANT  Rated at 1 WATT each.

Now when making left or right turns, the camera for that turn works.  I'm sure that can be a software improvement.  Some cars and trucks have this feature by default.  Like the Honda truck,

[West8]

New truck (2024) and new trailer (2023) with the same issue as described by Wxman post from April 1, 2021. I towed this trailer with my old 2006 Silverado 3 times without any issues. This past weekend was the first tow with my new truck. Drove 1.5 hours each way and got 50 to 60 "Check Trailer Wiring" DIC messages, each way with intermittent trailer break loss. I called a mobile RV repair service who determined that the issue is not with the trailer or connection. I'm taking the truck into GMC service next week. I will post updates as available.

 

[Lance S]

West8 - Keep me posted with what you find.  I have the same issue currently with my 2024 GMC Denali 2500 with a new 2023 Rockwood Minilite trailer.  On my first trip, I got the "Check Trailer Wiring" on the DIC.  The camper dealership attributed it to a connection issue with the 7-way connectors and the truck.  After "pushing" the pins together in the 7-way, it seemed to fix the problem for about two weeks, then the message returned.  The camper dealership used dielectric grease in the 7-way, same issue.  Replaced the 7-way connector on the trailer and did some basic testing of the braking system (by measuring the amps to the brakes when the emergency pin was pulled out) - the same problem.  We then replaced the 7-way receptacle/plug on the truck and the same issue returned.  

 

For better or worse, I decided to head to the campground with the DIC message occurring constantly.  After about 45 minutes of driving, the DIC message stopped and hasn't happened again (the drive back was about 2.5 hours).  I have an appointment at the GMC dealership to see if they can diagnose anything on the truck.

 

Side note:  The lights worked all the time.  On the dash, I put the trailer gain setting up, which made it easier to tell if the brakes were working or not. 

 

Edited August 22, 2023 by Lance S

[Gator888]

Possibly related to a power back feed, do you have solar panels on the trailer? Check out this thread: