2009 Sierra trailer brake

Abe Armendariz · November 6, 2019

Recently purchased a 2009 GMC Sierra 2500 HD with the LMM motor. I hooked up a dump trailer yesterday that typically works on all of my other vehicles. The integrated trailer brake control doesn't seem to be working. The lights all function on the trailer as they should. But I have to cycle through the information in the DIC to pull up trailer brakes. The gain is stuck at 0.5 and cannot be adjusted. It is followed by a series of dashes. I have checked stud 2 and the Itcb fuses. And replaced the brake controller itself. I'm wondering if the master cylinder sensor would be my next stab at the problem. Or if anybody might have any suggestions.

davester · November 6, 2019

I would first see if there are any codes generated by the braking or TBC systems. Probably will need to go to the dealer or a mechanic to do this, as the regular handheld units likely won't read codes from those systems...

swathdiver · November 6, 2019

Right, need scan tool that can read Chassis codes like the Tech-2. Besides the wiring and plug, there is the controller on the dash, the computer module mounted somewhere on the frame and a solid state relay also mounted somewhere on the frame. Recently replaced my SSR and all is well now, but my symptom were not like yours. If the module has to be replaced, it will require programming by the dealer or someone with a Tech-2 and a subscription to ACDelco's TDS system.

Abe Armendariz · November 7, 2019

Going to check with dealer tomorrow. Thanks I'll keep you all posted.

Abe Armendariz · November 9, 2019

No codes related to the trailer brake.

swathdiver · November 10, 2019

17 hours ago, Abe Armendariz said:

No codes related to the trailer brake.

That doesn't make any sense. When the new Trailer Brake Control module was replaced, was it programmed to the truck? It is not plug and play.

Abe Armendariz · November 11, 2019

Just replaced the switch on the dash not the module.

swathdiver · November 11, 2019

5 hours ago, Abe Armendariz said:

Just replaced the switch on the dash not the module.

Well, there are three components that make up the ITBC and it interfaces with the BCM, ECM, TCM and ABS modules, truly integrated! A basic code reader will not see these types of codes, it must be a bi-directional scan-tool like the Tech-2, Span-On Solus, MDI2, etc. You probably need a new module but if it were mine, I would first check all the connections under the truck and use my Tech-2 for diagnostics before replacing anything.

A man cannot rightly work on his truck without a scan-tool anymore, it's become more important than his wrench.

Edited November 11, 2019 by swathdiver

Abe Armendariz · November 15, 2019

So I got my truck back tonight. A mechanic went through scanned it and replaced both the relay and the trailer brake control module. He then had the truck taken to the dealership to flash the new module. I picked it up went and plugged it into trailer no communication between the controller and the brakes. I still cannot adjust the gain buttons, instead of .5 it reads. 0. Does not indicate trailer connected and cannot adjust anything.

swathdiver · November 15, 2019

10 hours ago, Abe Armendariz said:

So I got my truck back tonight. A mechanic went through scanned it and replaced both the relay and the trailer brake control module. He then had the truck taken to the dealership to flash the new module. I picked it up went and plugged it into trailer no communication between the controller and the brakes. I still cannot adjust the gain buttons, instead of .5 it reads. 0. Does not indicate trailer connected and cannot adjust anything.

Does your RPO sheet have JL1?

newdude · November 15, 2019

Was the relay on the frame rail replaced?

newdude · November 15, 2019

Any brake warning lights? Does it say service trailer brakes in the DIC? What type of brakes does the trailer have? Does the cruise control work on the truck?

Edited November 15, 2019 by newdude

Abe Armendariz · November 15, 2019

The RPO sheet does show JL1. The relay on the frame was replaced. No DIC warnings. Does not show that I have a trailer connected at all. But all lights work on my trailers. I tested four trailers all magnets drum trailer brakes. Works on three of my other work trucks. I can get to trailer brakes through the information button but cannot adjust it. Last night I checked all seven pins to see if maybe somebody wired it Goofy for their own trailer. Not the case. And the cruise control does work. I'm wondering how the truck knows there is a trailer connected? I wonder if that's the root of the problem?

Edited November 15, 2019 by Abe Armendariz

swathdiver · December 7, 2019

On 11/15/2019 at 10:02 AM, Abe Armendariz said:

The RPO sheet does show JL1. The relay on the frame was replaced. No DIC warnings. Does not show that I have a trailer connected at all. But all lights work on my trailers. I tested four trailers all magnets drum trailer brakes. Works on three of my other work trucks. I can get to trailer brakes through the information button but cannot adjust it. Last night I checked all seven pins to see if maybe somebody wired it Goofy for their own trailer. Not the case. And the cruise control does work. I'm wondering how the truck knows there is a trailer connected? I wonder if that's the root of the problem?

Any progress on this? Have you tried a trailer with a different kind of brakes? On another forum a fella hooked up an aftermarket controller while leaving the hot wire for the JL1 still connected at the fuse box and burned something up. He never did respond if memory serves, too proud I guess.