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The 'service trailer brake system' in DTC / ABS light come on. At one point in time i was getting a UC121 code but i havent seen it in a while... just the lights.
Things i hae done to try to fix it:
Taken to dealer- they replaced the ignition? -$300 lasted 3 months before lights came back
Replaced front ABS Sensors
Checked/replaced hubs
replaced brake pedal switch - lasted another 3 months
Checked just about all the wiring related to trailer brake system, cleaned connections

the lights have been on consistantly all summer but since ts been chilly here for the past week theyve been gone... leading me to believe its temperature related.

The only time it would go away when hot outside would be when i drove with the AC on for 10 min and make a quick pit stop... when id restart, it would be gone.
Therefore i thing the problem is temperature related, and inside the truck. My current theory is that the increased temp in the cab causes an increased resistance in the brake pedal switch/sensor leading to the fault. im still waiting on the new switch to come in and will keep u guys updated
 

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any update? I have the same thing going on. ABS light, Brake light, service 4-wheel drive, service brake lights, all intermittently and all of the sudden.
 

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ABS Light and "Service Trailer Brake System" Message in DIC - FIXED

I had this same problem. For about three months, any time I would take a sharp right turn, the ABS light would come on and the "Service Trailer Brake System" Message would pop up in DIC. As soon as I straightened the wheel, it would go away. One day on the interstate, both the light and the message came on and stayed on. When I got home, I plugged in my work trailer and didn't have any brakes.

To the point: the fix = right front ABS wheel speed sensor

I made an appointment with the dealer ASAP since I needed my trailer later in the week and didn't have time to find the problem myself. They told me it was the ABS sensor and the master cylinder pressure sensor... $525 altogether. I found it mighty suspect that they both went out at the exact same time (the integrated brake controller needs both to function properly), but I didn't argue because I needed it working. Turned out they couldn't get the parts in time, but they sure still tried charging me a checkout fee. Anyway, I got home and climbed into the tire well to have a look for myself, and there was a frayed wire sitting right on top of the hub. I stripped it and spliced them together as best I could (the material GM uses to coat those wires is a b*tch to strip, especially with dull strippers), and it fixed the issue. If you have the same problem, you have to drive the truck a few feet to get the sensor to register and turn off the ABS light. Needless to say, I'm a little upset with my dealer for recommending a $300 job (the master cylinder pressure switch) that absolutely didn't need doing.

Ron Nielson made this post over in the towing and hauling section of the forum describing how the integrated trailer brake system works, and I found it extremely helpful while I was researching:

Copied from another source:

Trailer Brake Control System Description Summary
There are 3 main components to the Integrated Trailer Brake Control System (i.e. The Trailer Brake Control Switch (TBCS), the Trailer Brake Control Module (TBCM ), and the Trailer Brake Control Relay
(TBCR).) There are three other primary inputs to the TBCM. Two come via the Serial Data Network. One is directly wired to the TBCM. The inputs coming via the Serial Data Network are the Wheel speed data and the Master Cylinder Pressure Sensor’s pressure data. The Master Cylinder Sensor input is indirectly used by the TBCM to scale the trailer braking in relationship to the pressure placed on the foot pedal. The wheel speed data is indirectly used to validate the brake signal and validate related errors. The Stop Lamp Switch is directly wired directly the TBCM and used for a calculation to double check whether you are really pressing the brake pedal, among other things. Also, with a data communications network involved, the Engine Control Unit is also involved as it is managing the communications of the network. There are several codes that can be generated by the ECU and the TBCM. (This is why it is best to start ITBC troubleshooting by reading the vehicle’s codes.)

There are also, other inputs to the TBCM (e.g. like the ignition circuit, the TBCS, etc.) Several of these are used for other diagnostics and tests made by the TBCM’s program. Each of these inputs will generate a code, if a failure is detected by the TBCM, ECM or the BCM. The TBCS is used to adjust the gain and manually activate the Trailer Brakes. There is an output to the Driver Information Control display panel to show a trailer connection and gain settings, etc.. There is another output to the Trailer Brakes (i.e. The TBCM tells the TBCR how much voltage to apply to the trailer brakes, based on the amount of Brake Master Cylinder Pressure being applied to the vehicle’s brake system.)

Component Locations
The TBCM and The TBCR are located on the inner driver side frame rail near the rear tire under the cargo box. The TBCS is on the lower dash. The Master Cylinder Pressure Sensor is located on the Master
Cylinder, under the hood. The Stop Lamp Switch is located near the brake pedal.

Component Programming
The TBCM has an internal program in it to facilitate the data communications and scale the braking, and control the TBCR, among other things. If the TBCM is ever replaced, it has to be reprogrammed.

GM’s Integrated Trailer Brake Control System Description
Component Powering (Two B+ Circuits)
For the first B+ circuit, there is a Red/Black wire that needs to be connected to Stud #2, which is on the front of the under-hood fuse box. Fuse 58 fuses this circuit. If the fuse is installed and working, you should see >+12VDC on Stud 2. This provides power to the TBCR. When the TBCR is switched on by the TBCM this +12 VDC is indirectly fed to the trailer brakes via the TBCR. This wire typically comes hooked up and fused. However, on some models it may not have been hooked up and/or not fused. Now here is a catch, … There are three Red/Black wires near the under-hood fuse box. Only one goes to the Trailer Brakes. Two are Aux Power for charging trailer batteries. The two Aux power wires are
typically taped up to wiring harnesses. The Red/Black wire for the Trailer Brakes typically comes hooked up to Stud 2. (Mine was hooked up.) If the ITBC system’s Red/Black wire is not hooked up, then you have to find it and hook it to Stud 2. But, do not confuse it with the other two Red/Black Wires used for Aux Power.

The two Aux power wires are located as follows: There is one Red/Black Aux Power wire taped to the harness between the fender and under-
hood fuse box. (This wire was even labeled Aux Power on mine, which is confusing because it is not the Aux Power wire to the Towed Trailer connector on the rear bumper.) This one powers the Aux Power to the portion of the trailer harness that feeds the front of the Cargo box for 5th
wheelers/campers. An added harness has to be plugged in for this, on the other end. This is not the wire you need to fully power the ITBR.
The second Red/Black Aux Power Wire is taped to a wiring harness between the under-hood fuse box and the engine. It may actually be right under the fuse box. Mine was. Again, this is not the wire for the TBCM. This is an Aux Power wire that runs all the way back to the trailer
connector to charge a towed trailer’s batteries. This is not the wire you need to fully power the ITBR. (If you want to hook up either one of these to charge batteries, you hook it to Stud 1 and fuse it with 40 Amp fuse.)
So that leaves a third Red/Black wire to power the TBCR. This remaining Red/Black wire has to be hooked up to Stud 2 and fused. If it was not hooked up by the manufacturer, then it is taped to a harness someplace close to the under-hood fuse box. It gets hooked up to Stud 2 and fused with a 30 amp fuse.

There is a second B+ circuit that needs to be energized for the Trailer Brake System to work. This is a Red/White wire. This wire is already hard wired to the under-hood fuse box. However, Fuse 19 fuses this circuit. This fuse typically installed by the manufacturer. But, check it to make sure it is still good.

GM’s Integrated Trailer Brake Control System Description
ITBC system Troubleshooting

To troubleshoot w/o a Tech II, all you can do is check the connections and look for the B+ voltages at each of the three main components. So, you check all grounds at all three components. Then you check the Red/Black wire at the TBCR and the Red/White wire at the TBCM for +12VDC. You also can check the serial data connector contacts, but I doubt that these are a problem because the truck is new. If the ITBC system is NOT working on delivery, I suspect that the Red/Black wire for the ITCR is not hooked up or a fuse is missing.
If you have all the fuses in and the correct Red/Black wire fused and attached to Stud 2, then I would say it is time to go into the dealer to get the codes read. It is difficult to get on all the grounds and B+ wires
for testing and why spend all that time and effort only to find out the BCM or ECM, etc may be at fault.

If the trailer works on another truck, it is safe to assume the trailer is not the problem. However, this does not rule out a problem in your truck’s trailer connector. The truck’s connector is subject to moisture and the resulting corrosion. My trailer’s running lights blew a fuse because of moisture in the connector, the third week I had the truck. Most of the time trailer brake problems are found at the connectors or the other end of the trailer’s harness. Also, trailer brakes often short in the trailer wheels. That is why fuse 58 in the truck is there. Sometimes the trailer harness also loses it connection in the Junction box located someplace on the
trailer (at the other end of the harness.)

I wrote about GM’s Red/Black wire fiasco in a RV magazine. Check out the bottom part of the Article that results from the below link. But, this document has far more detail. RVing with Len Todd - Better RVing
 

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I am back to the drawing board. I now have two new front hubs, two new abs sensors, a new left brake caliper (mine locked up last week, turns out it was deriving from another issue though) and a new in-cab brake switch. I still am getting the exact same issue at random:
Service brakes
Service 4-wheel drive
Service trailer brakes
ABS light
Brake Light

They come and go at random and almost seem to go away if I hit a hard bump or pothole. I have been chasing this problem since January and cannot figure it out. I am towing a 13,000 lb trailer tonight and would REALLY like to get it handled before then as I cannot afford to lose trailer brakes during this haul.

I am going to check into my fuse box this morning, but any suggestions would be wonderful.
 

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Sounds like a wheel speed sensor. Had a similar issue on my 11. Rear wheel speed sensor fixed it.
 

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I have the part due in at 1:00, where is the rear wheel speed sensor on the truck, I checked pumpkin and did not see any sensors on there. Thanks for your help, I hope this works!
 

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Follow this wire to the back side of the wheel. Mine looks a little different because it has lift blocks and bags but you'll see it. Undo the connector on the wire and the wire clips, undo the two bolts on the back of the hub, replace, drink beer.
 

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Mine looks a little funny because I made shields for my sensors for the logging road rocks but that's the sensor.
 

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I have a 08 CC DRW 2wd. My "Service trailer brakes soon" DIC comes on only when the 7 way plug inside the bad gets wet. But my trailer brakes don't seem to work as well as they should. I can manual hit the brake controller, but very little resistance on the trailer brakes. Any ideas on this problem? No ABS lights or anything else.
 

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Dirty-Max, my rear wheel speed sensor was actually in my transfer case, none on the rear wheels themselves. I replaced the part as I was walking out of the door and then about 10 minutes down the road, same thing, all the lights again. They went away after about 10 seconds and haven't been on since. I am now going to focus my attention to the fuse box, there is most definitely some correlation with hitting bumps and triggering or turning off the indicator lights.
 

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Hmm interested sorry for the miss information. That seem very strange, I wonder how it works without being able to get each individual wheel speed? Anyway, hope you get it figured out, I had the exact same symptoms with my failed sensor. I would run the truck and have a buddy wiggle the sensor wires to see if its a damaged Wire.
 

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I had the same symptom, the front passenger inner fender was hitting the mounting for the sensor cable on the control arm when the suspension worked. It broke the mount, and would show the abs fault then the trailer brake fault when the suspension worked. I trimmed the inner fender and attached the cable to the broken mount with a couple of tie wraps. 'Hoping the cable will live as long as the bearing assembly now...
 

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I am having the EXACT SAME ISSUE as you on my 2009 gmc DURAMAX. if I hit a bump or pot hole all the lights come on. I wish I know what the problem was. keep me posted please. I need a fix.
 

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If your ABS light is on , that will, in turn, cause your SERVICE TRAILER BRAKE SYSTEM message to display on the DIC. Fix the ABS problem and the DIC message will stop. The Trailer brake system requires a working ABS system in order for it to work.
 

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I had a similar issue and found a broken wire I think it was yellow in the loom above the fuel tank where it had been loose and moving around repaired wire and relocated loom to solve problem it actually shut the engine down when we hit a rough patch on the road which was not good on the freeway at speed towing with not much area to pull up in a hurry , also I would check the trailer plug terminals as they may have come loose
hope you have solved the issue
regards
Steve
 

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Well.

I took it to my local chevy dealer and have a few answers. Turns out i DO have a front left wheel hub going bad and a right front axle boot leaking. So that is all getting fixed. Not sure if it will solve my ITBS issues, but will see when I go to pick it up.

Snappy are u suggesting that I disconnect my battery cables, then hold them together to somehow reset the TBS??

Not quite following that one.

Thanks to everyone for the awesome advice, always can count on die hard chevy guys.
Was this the problems??
 
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