06 Dmax trailer brake issue

rpf500 · Jul 22, 2015

Guys,
just got a new to me truck. Guy put a new trailer brake controller on because old one was messing up. I think it's a fuse or wire. I don't know what fuse controls the brakes though. Hooked trailer to my DD and all is well. On the dmax all lights, signals, etc work when hooked to trailer just not the brakes.

Any ideas? Oh......controller shows an "nc" code. No connection.

rpf500 · Jul 22, 2015

Oh....and I have power with a test light on the trailer drums. That makes me even more confused. Unless I have an open circuit somehow. :dunno:

TBItoy · Jul 22, 2015

There is a trailer brake fuse, IIRC it is in the panel on the driver side of the dash (the trailer light fuses are in there)

rpf500 · Jul 22, 2015

Does this make sense?.....if I have power at the brakes and all trailer lights work, it can't be main wiring or fuse.

I'm googling what the factory plug wires go to. (under dash). He matched the 4 wires up with like colors but that doesn't mean it's correct. I have the controller instructions for what each color does, just need to find what GMs colors mean.

In my mind it seems everything is in order on the truck and trailer I just don't have the controller activating brakes.

al1tonyota · Jul 22, 2015

rpf500 said:
Does this make sense?.....if I have power at the brakes and all trailer lights work, it can't be main wiring or fuse.

I'm googling what the factory plug wires go to. (under dash). He matched the 4 wires up with like colors but that doesn't mean it's correct. I have the controller instructions for what each color does, just need to find what GMs colors mean.

In my mind it seems everything is in order on the truck and trailer I just don't have the controller activating brakes.

Sounds like a ground problem! ESP if you are getting power!

CHASMAN9 · Jul 23, 2015

There is a wire next to the fuse panel under the hood that has to be connected in order for the controller to work. It is installed from the factory, but for some reason they do not hook it up and let the owner do this. I had this problem on my 2010. Maybe this will help? :dunno:

wont work · Jul 23, 2015

al1tonyota said:
Sounds like a ground problem! ESP if you are getting power!

This. Check your ground side

rpf500 · Jul 23, 2015

I'll check it over. I hate wiring issues!!!

I still can't wrap my hands around how everything works fine on truck and trailer minus the brakes. I'm wondering if the brand new controller could be bad. I can try to throw it in my DD and test it that way I guess.

I am really thinking it's something to do with the controller, or wiring to the controller. Guy swears to me that the brakes on his RV worked perfectly fine and that he is sure the old controller was bad so he bought this new one.

rpf500 · Jul 23, 2015

Anyone know if the blue wire coming from factory plug under dash should fully light up a test light? IE...like it does to the black wire.

Mine lights up but is dim. Doesn't get brighter by applying the brakes either.

r_young · Jul 23, 2015

It should not. When you check that wire it should just set off the controller. The blue wire is what sends signal to your trailer.

rpf500 · Jul 24, 2015

r_young said:
It should not. When you check that wire it should just set off the controller. The blue wire is what sends signal to your trailer.

OK, checked this one again. When I test it from the fuse panel under the hood, it is NOT hot until I hit the slide button on the bottom of the controller. So, I am thinking that is all good. At the back of the truck, it works the same way so I assume no wiring issues on the truck.

What is screwed up is that when I hook my DD to the trailer it works fine so that makes me think it's the truck. But testing wires makes me think it's the trailer. This is so f'd up. Did I mention I hate wiring issues?

Oh, and this morning I get a CEL light that is code P0504 which is a brake switch code and can be set off by the aftermarket controllers. So I maybe need a brake switch or maybe not and all my messing around with this set that light off. :dunno:

monster · Jul 24, 2015

is dd and new to you truck wired the same at plug for brake power?

muddinmetal · Jul 24, 2015

CHASMAN9 said:
There is a wire next to the fuse panel under the hood that has to be connected in order for the controller to work. It is installed from the factory, but for some reason they do not hook it up and let the owner do this. I had this problem on my 2010. Maybe this will help?

This, it is a folded up wire between the fuse block and the fender, labeled with a tag that says trailer brake. Check that this is hooked up first

rpf500 · Jul 24, 2015

muddinmetal said:
This, it is a folded up wire between the fuse block and the fender, labeled with a tag that says trailer brake. Check that this is hooked up first

I'll check it but I ASSume it is hooked up since the PO pulled a camper with the truck and said the brakes worked fine.

muddinmetal · Jul 24, 2015

rpf500 said:
I'll check it but I ASSume it is hooked up since the PO pulled a camper with the truck and said the brakes worked fine.

A lot of people hook up the wrong wire that is closer to the box than this one is

rpf500 · Jul 24, 2015

muddinmetal said:
A lot of people hook up the wrong wire that is closer to the box than this one is

Awesome! I'll check for sure when I get home.

r_young · Jul 24, 2015

The wire next to the fuse panel is on the 07 and up. It sounds like the under dash harness is not right. I néed more info though. It would be easier to just talk you through it if you are interested. Let me know.

rpf500 · Jul 24, 2015

r_young said:
The wire next to the fuse panel is on the 07 and up. It sounds like the under dash harness is not right. I néed more info though. It would be easier to just talk you through it if you are interested. Let me know.

PM sent.
Buddy hooked up his truck to my trailer, all is fine. Same on my DD.

That tells me truck issue.

erok131 · Jul 27, 2015

I've heard of this being a common problem with the duramax. Mine acts the same but will randomly start working for a week or so and then the same thing. Everything works but brakes. My buddy bought a 2015 and would constantly beep and tell him trailer disconnected on the dash and he would have no power to brakes.

rpf500 · Jul 27, 2015

Well, I'm still on the hunt. Now, my DD is throwing the same codes as the truck is so that is telling me trailer. It's so ****ed up. I'm rewiring the trailer tonight so I can be 100% sure on that part. If I find an issue, then it will be purely a coincidence that the trailer is the problem. I know for certain I pulled this trailer just a week ago to go pick this truck up and the brakes worked fine all the way to St.Louis. I'm now hoping that a wire on the trailer got messed up toward the end of the trip when I wasn't paying attention to the controller. Then, when I unhooked my Tahoe and hooked up the new truck, is when I noticed the problem. If rewiring the trailer tonight doesn't work, then I don't know what's next. I need to go visit one of my wheelin buddies and hook to their trailer. That would be the next logical step. Maybe one I should have done already I just don't live near any of them.

Sorry for the rant.

And if any of you all ever need wiring advice, hit up r_young on here. Dude knows his ****. Knows all the wires colors, locations, etc. He has been a HUGE help to me!!