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Old 09-09-2020, 01:40 PM   #1
John R
Join Date: Jul 2012
Location: Traverse City,Michigan
Posts: 40
Trailer message trailer not connected

I have a new to me 2016 GMC 2500hd Denali. When hooked up to my fifth wheel, the info screen will alert the check trailer connection it then shows trailer connected. When this happens all the lights are working and I check the brakes and they are working, I've had it checked twice but still acting up. Anyone know whats going on?
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Old 09-09-2020, 01:47 PM   #2
Texas Steve
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On my 2019 Silverado 2500 HD, I have to turn the truck off before plugging in the 7-pin connector otherwise it gives me the trailer not connected message. Turn off truck, plug in trailer cord, re-start truck. Might give it a try on yours. Good luck...
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Old 09-10-2020, 06:25 AM   #3
John R
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Thanks i'll try that
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Old 09-10-2020, 07:54 AM   #4
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check plug too - my Silverado had "check trailer" a couple times. Dirty/corroded plugs may create that message intermittently.

Congrats on truck - I love mine!


2019 GMC Sierra 2500HD 6.0L
2020 Cougar 32BHS
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Old 09-10-2020, 08:46 AM   #5
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Also, the wiring harness is a "modular design" meaning that the same wiring harness is used for trucks with/without the 7pin/4pin connector. There is a "plug on the truck harness" behind the bumper. The trailer connector you see on the bumper plugs into that harness. There may be corrosion/water in that plug. So, crawl under your rear bumper, disconnect that plug, let it dry, apply di-electric compound to the terminals and re-connect it.

In Ford/Keystone combinations, there has been some history of "plug mismatch" between the truck 7 pin and the trailer 7 pin connectors... Ford's plugs are manufactured by one company and Keystone's "low bid umbilical harness".... A slight difference in tolerances between the truck/trailer connector pins can sometimes cause a problem with "computer monitoring of the connection".... I replaced the trailer 7 pin connector with a "quality aftermarket plug" and it solved all of my "disconnect messages"....

I'd first crawl under the truck and check that connector, then consider changing out the trailer umbilical plug for a "better, more reliable brand".

ALWAYS, ALWAYS keep di-electric grease on all exposed metal ends of both the truck and trailer connectors !!!!!

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Old 09-10-2020, 09:07 AM   #6
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My 2015 GMC had a recall for this. Maybe check if there is one for newer trucks and HD.
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