[LMMDually]

My service trailer brake system message stays lit up, and I need to fix it because I pull a lot of trailers, and it is rather nice to have some stopping help. So far I have just checked the wire (dark blue) that says its the trailer break with a hot wire tester at the rear of the pickup close to the plug in the bed and at the bumper, I get no fire anywhere.

So I take it down to the dealer today, and I recently had my abs light come on (due to right front wheel speed sensor) guys at the dealer say that the sensor is my whole problem and it will fix everything when I replace it. I tell them that the service trailer deal was on way before I had any abs light come on. They treat me like Im stupid an charge me 44 stupid dollars for "diagnosing" it and telling me I had a wheel speed sensor out. So I go back to the shop throw on another wheel speed sensor that I had laying around, and wham no abs light an still trailer brake system light. I was frustrated so called the dealer back an they said they would knock off the 44 if I bring it back to them for them to fix it.

Sorry for all of that, but does anyone have any ideas of what else to look for?
I have already checked fuses an stuff as well.

Thanks, Corey

 

[TroyD]

Yup dealers completly piss me off too had some bad experiences, but my 09 work truck does the same thing it will flash check trailer brake wiring but usually only when its wet out and not all the time, I also have had the trailer brakes completly not work on a 3 hour ride towing a small back hoe, took it into the dealer and they said nothing is wrong with it and couldnt get it to act up, i wish you luck brotha

 

[DatCajunLMM]

have you calibrated for larger tires, these sensors will see even a slight difference and throw different lights

 

[TroyD]

No i have not i am running a 265 now over stock so only one size, how would i calibrate that with out a tunner consider its a gas engine work truck, and why would that have to do with the trailer braking? Or are you talking for the abs sensor?

 

[DENALI HD3500]

O.K. First off you will see no power at rear (blue ) trailer brake wire with a test light or hot wire tester on the new IBC system. You need to use a DVOM. Seems like you have a bad ground wire. check this first.

 

[Retired Fire Captain]

Same problem took it to the dealership and under warranty they covered it on my 2008. Check service document 2066487. ct 7521, 944, 945. Teck replaced trailer brake relay and all is well with the world now!

 

[Duramaxxx6.6]

My cousins truck is the same way... Dealers still haven't figured it out...

 

[LMMDually]

Btw sorry I posted in the lml section guys. Ah thanks for that info denali duramax. Yes I have recalibrated for my lager tires. Sorry that you are having this trouble too TroyD. Ya I pulled a 15k tractor on a gooseneck about 200 miles away today and trailer brakes would have been nice lol

 

[christrussakis]

all I did was forget to hook the abs wire back up on the right front hub before I cranked the truck!!! now I can't get the lights to go back off!!!!! I have been to parts store and they used there abs coder and I would not clear it!! went somewhere else and the same thing all it says is no communication with scanner??? don't know what to do!!! what if I disconnect both batteries??? can anyone help???? thanks!!!

 

[SuperBlackTruck]

I got the same code one time this winter when it was really cold.

 

[dougmac]

Btw sorry I posted in the lml section guys. Ah thanks for that info denali duramax. Yes I have recalibrated for my lager tires. Sorry that you are having this trouble too TroyD. Ya I pulled a 15k tractor on a gooseneck about 200 miles away today and trailer brakes would have been nice lol

While they were busy "diagnosing" your trailer brake light, did they happen to tell you what trouble code was causing the message to display?

 

[Jleviste]

If you don't want to read this go to the bottom for possible solutions

The 2016 GMC Denali 2500HD like many other of the new LML's have the same issue as you stated above. My father had the same issue; one day we tried retuning the truck (if you have a tune) while the trailer is unhooked, then hooking the trailer back up, and pulling all of the fuses out, finding that worked; it just so happened the other day, the same issue popped up. Again like most said it's most likely not the truck at all, we found out that the 7 pin trailer plug may have corrosion possibly limiting the flow, so we cleaned it out by using sand paper, then we put WD-40 in the Truck's outlet to get rid f water, we thought maybe if water got in it could short it, again we don't know we are trying many things, but it still didn't work, even if it didn't it was still nice to service those two. Now after we took a look at the box that controls the trailers lights and braking system, we saw that some of the wires were touching or were too close together, we pushed them aside and tightened everything back up. Already mad enough we were hoping it would work, and that notification "Trailer connected" and the test of the trailer brakes changed our moods.

Solutions: Check with a programmer to see if the truck is throwing any codes, if not try cleaning your 7 pin trailer connector with WD-40 and get rid of corrosion with some sore of small file, DO NOT FILE THE TRUCK PORT, If that does not work, check the trailer's "power box". Tell me if this helped

Truck Specs (Race Tune from Duramaxtuner.com's Spade tuner)
-2016 GMC Denali 2500HD
-1100 ft-lb of Torque
-620 HP to wheels
-Race Tune from Duramax Tuner's Spade tuner
-Fass Fuel Systems
-Emissions Equipped (We ain't no tree huggers, We just love the warranty)
-1/4 mile times low 13's
-0-60mph in 5.4 seconds

Contact me if you have any questions