Truck showing no trailer connected.

[PaulEC]

I got a 2020 GMC 3500. 
Having a problem with the truck recognizing some new trailers and not others. 
With the trailer connected, the screen will show no trailer connected but all lights on the trailer work. But not the trailer brakes. 
Had the truck tested at a dealership yesterday and no issues found. 
I called Jayco and Grand Diesign. 
They both say some trailers are different. 
GD had no recommendations. Jayco claims that an after market brake controller is needed. 
I looked it to this option to be told it will throw codes and void the warranty. 
Called GMC, someone is supposed to be getting back to me. 
Has any other GMC owned ran in to this issue. 
If so how did you correct the problem?
Thank you in advance.

[unit]

Some trailers with all LED lighting don't draw enough current to let the truck know it's there.  I had this problem with my 2018 Airstream trailer with all LED lighting.  The truck would see the trailer when first connected to the truck then lose the connection after I'd stopped and turned the ignition off.  The problem was random and unpredictable.  Like you, my lights and brakes all worked even though the truck was displaying the message.  However, the trailer TPMS system did not work and the truck did not accumulate trailer mileage when it was not recognized.

 

I read about Ford truck owners having similar problems on a Ford forum and found this 7 way plug adapter resolved their issues.  I bought one and it works for me.  I have not had a 'No trailer connected' error since.  The plug apparently works by adding resistance to the lighting circuit.  It's not expensive and might be worth a try.

 

https://www.amazon.com/gp/product/B00C4AYR3U/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

Edited November 6, 2021 by unit

[PaulEC]

For the money it’s worth a try. 
I just ordered it. 
thank you. 

[XY74]

Mine does the same thing with my flatbed trailer that has LED lights.  On your first picture, if you hit the "trailers" tab, it will show the list of trailers you have saved.  Select the appropriate trailer and it will then say "connected to trailer A" or something along those lines.  It will also sometimes give me the check brake light message randomly when they are working fine.  I have had zero issues like this with my RV that is NON LED.  Let us know how the adapter works.