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Hey all. I have been fighting with my trailer brake system for the last year or so. I have REPLACED the following: Brake pressure sensor on the MC, trailer brake relay under the bed, brake light switch at the pedal. I dont get the message until i step on the brake pedal and release, and lately it has only been under heavy pressure, if i just tap on the brakes with a trailer hooked up they work fine. I get this message whether i have a trailer hooked up or not. Another VERY WEIRD symptom, my cruise control will NOT work unless i trigger the "service trailer brake system" message and then cruise works just fine. I have traced wires and everything looks good. I do have the bundle under the front of the bed, but even with the plug(and that bundle, disconnected i still get the message. I have a brand new Prodigy P2 that i can install, but id really rather use the ITBC. Anybody have any ideas? Im at a complete loss at this point.
 

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I would try replacing the brake pedal position sensor. My trucks started acting up with this crap, but my truck threw code P0571 dealing with cruise control, but i have seen where the "service Trailer brake System" can come on with it as well. I ended up clearing the code with my edge and pulled up on the brake pedal to get my cruise to work again. Waiting to see if the light comes back. If it does I will replace the brake pedal position sensor. Ive also read where its been a simple brake light bulb out. Just search that P0571 even though your truck is not throwing that code and you will get some more knowledge on how all this BS intertwines.
 

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Have you scanned for codes, both history and current? If so, what are they are history or current. Is your ABS light on in your dash? If so, that needs to be fixed, TBCM cannot operate while there is an ABS error. Check your hi mount brake light - if not operating, fix that.



Here is some basic info about Cruise Control:
Cruise Control Description and Operation

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions at speeds above 40 km/h (25 mph). Steep grades may cause variations in the selected vehicle speeds.

The following are the main components of the Cruise Control System:



  • The accelerator pedal
  • The stop lamp switch
  • The body control module (BCM)
  • The cruise control switches
  • The engine control module (ECM)
  • The throttle actuator control (TAC) motor
  • The vehicle speed sensor (VSS)
Cruise Control Engaged

The Cruise Control System will engage and adjust vehicle speeds, based on the activation of the following cruise control switches, which are located on the steering wheel:



  • The on/off switch
  • The + RES switch
  • The - SET switch
The body control module (BCM) monitors the signal circuit of the cruise control switches. The BCM relays the cruise control switch status to the engine control module (ECM) via the GMLAN serial data circuit. The ECM uses the status of the cruise control switch to determine when to capture and maintain the vehicle speed. The ECM monitors the vehicle speed signal circuit in order to determine the desired vehicle speed. The ECM uses the throttle actuator control (TAC) motor in order to maintain the vehicle speed. For further information on the TAC System, refer to Throttle Actuator Control (TAC) System Description for the 4.3L engine or Throttle Actuator Control (TAC) System Description for the 4.8L, 5.3L, 6.0L, 6.2L or 7.0L engines.

Voltage is supplied to the cruise control switch via the steering wheel control switch reference voltage circuit supplied by the BCM. The cruise control function switches are arranged in a resistive ladder design, with each cruise control function switch having a different resistance value. The BCM detects a specific voltage value that is associated with the cruise control function switch being activated. When the normally open cruise control on/off switch is turned ON, the switch closes and the BCM supplies a ground to the cruise control switch ON indicator circuit as it becomes illuminated. The BCM sends a GMLAN serial data message to the ECM indicating that the on/off switch is active. Similarly, when the normally open + RES switch or the normally open - SET switch are pressed, the switch closes and the BCM detects the predetermined voltage signal on the cruise control set/coast and resume/accel switch signal circuit. The BCM sends a GMLAN serial data message to the ECM indicating that the + RES switch or the - SET switch is active. To engage the Cruise Control System, ensure that the vehicle speed is above 40.2 km/h (25 mph), turn the cruise On/Off switch ON and momentarily press the - SET switch. The ECM will engage the Cruise Control System and record the vehicle speed. The ECM sends a GMLAN serial data message to the driver information center (DIC) in order to illuminate the CRUISE SET TO ### message. The ECM sends a GMLAN serial data message to the instrument panel cluster (IPC) in order to illuminate the Cruise Engaged indicator in the IPC. The - SET switch and the + RES switch will remain inactive when the BCM has not received the predetermined voltage signal from the on/off switch. Pressing the accelerator pedal, while the Cruise Control System is engaged, will allow the driver to override the Cruise Control System in order to accelerate the vehicle beyond the current set vehicle speed. When the accelerator pedal is released, the vehicle will decelerate and resume the current set vehicle speed. The driver can also override the current set vehicle speed via the - SET switch and the + RES switch. When the Cruise Control System is engaged, pressing and holding the - SET switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating the Cruise Control System. When the - SET switch is released, the ECM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the Cruise Control System is engaged, momentarily pressing the - SET switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments for each time that the - SET is momentarily pressed, with a minimum vehicle speed of 37 km/h (23 mph). Pressing and holding the + RES switch, when the Cruise Control System is engaged, will allow the vehicle to accelerate to a greater vehicle speed than the current set vehicle speed. When the + RES switch is released, the ECM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the Cruise Control System is engaged, momentarily pressing the + RES switch will allow the vehicle to accelerate at 1.6 km/h (1 mph) increments for each time that the + RES switch is momentarily pressed, with the maximum acceleration total of 16 km/h (10 mph) over the current set vehicle speed. Momentarily activating the + RES switch will recall the previous vehicle speed, after the cruise control system is disengaged by pressing the brake pedal or by activating the CANCEL switch.

Cruise Control Disengaged

The engine control module (ECM) disengages the cruise control operation based on the signals from the following switches:



  • The stop lamp switch
  • The cruise control On/Off switch
  • The cruise control cancel switch
The body control module (BCM) determines when the cruise control cancel switch is activated. When the normally open cancel switch is closed, the BCM detects the predetermined voltage signal on the cruise control function switch circuit. The BCM sends a GMLAN serial data message to the ECM in order to disengage the cruise control system.

The stop lamp switch is mounted on the brake pedal bracket. When the brake pedal is applied, the normally open stop lamp switch closes. The ECM monitors the stop lamp signal circuit through a discrete input and a GMLAN serial data message signal from the BCM indicating the brake status. When both signals indicate the brake pedal is applied, the ECM will disengage the cruise control system.

The Cruise Control System will disengage when the cruise control on/off switch is switched OFF. The vehicle speed stored in the memory of the engine control module will be erased when the cruise control On/Off switch is turned OFF, or the ignition switch is turned OFF.

The Cruise Control System will disengage when the ECM detects that a driver override function has been active for approximately 60 seconds. When the Cruise Control System has been disengaged, the ECM sends a GMLAN serial message to the instrument panel cluster (IPC) in order to turn OFF the Cruise Engaged indicator, and to the driver information center (DIC) in order to turn OFF the CRUISE SET TO ### message.

Each time the Cruise Control System is disengaged, the ECM will keep track of the reason for system disengagement. The last 8 disengagement reasons will be recorded within the ECM memory, and can be viewed with a scan tool.

Cruise Control Inhibited

The engine control module (ECM) inhibits the cruise control operation when any of the following conditions exist:



  • The ECM has not detected a brake pedal activation from the body control module (BCM).
  • A Cruise Control System DTC has been set.
  • The vehicle speed is less than 40.2 km/h (25 mph).
  • The vehicle speed is too high.
  • The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear.
  • The engine RPM is too low.
  • The engine RPM is too high.
  • The system voltage is not between 9-16 volts.
  • The Antilock Brake System (ABS)/Traction Control System (TCS) is active for more than 2 seconds.
 

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Discussion Starter #4
I scanned for codes, nothing. I don’t have an ABS light. Honestly I’ll live without my cruise control if my trailer brake system would work. The truck throws this message without a trailer even hooked up. I found a recall that covered contamination in the BCM when it was installed and it references this message as a common symptom. Funny though how when I pull my vin the recall isn’t listed, yet it’s on the national recall website and lists my model and year of truck. I’m about ready to just burn this truck to the ground and buy a dodge.
 

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It is ABSOLUTELY FRUSTRATING to have this problem. There are several common cures, and who knows how many non-common cures. It's a shame that GM hasn't provided a decision tree to help diagnose the problem. Without some guidance, we are left to our own imperfect devices to diagnose and fix the problem.

You wrote," dont get the message until i step on the brake pedal and release, and lately it has only been under heavy pressure, if i just tap on the brakes with a trailer hooked up they work fine. " That sure sounds like a brake light switch problem, and you said you replaced that. Did you use a ACDELCO switch" If not, i would invest in one. Many things for our trucks just don't work correctly with aftermarket parts. And I would lube my brake pedal pivot point so that the brake pedal goes all the way back to the top on release. I even pulled my pin out and greased it and turned it so that the wear marks were in a different position. Not at all sure it helped, but, along with other things I tried, I haven't had the problem in many years.

And the big elephant in the room, so to speak, is the TBCM itself, right next to the relay. You might get a wiring diagram of the two, to help you understand how these things work together. If you replace the module with new, it needs programming.

Personally, I think it's worth extra effort to have a reliably working antilock brake system, specially if you pull a trailer of any sort.
 

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I’ll throw this in from left field… it may or may not have a bearing on your issue.
I was having many of the Service Trailer Brakes messages over the years in my 2007.5.
They would arrive without any apparent reason and many times disappear for no apparent reason. I tried a lot of things posted on this forum to permanently fix the issue and I can’t say with any authority any of those fixes did anything.
Recently I had the body control module (BCM) completely fail. Just before it failed the only warning I got was Service Trailer Brakes.
The BCM communicates with the brake module and many other modules. The 2007.5 BCMs were known to be flakey too.
After replacing the BCM I haven’t seen any more warnings like Service Trailer Brakes. It hasn’t been very long since the module was replaced so I may get the warning in the future. As for now I’m thinking the Service Trailer Brakes warning might have been a result of lost communication between the BCM and the brake module.
 

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Discussion Starter #7
It is ABSOLUTELY FRUSTRATING to have this problem. There are several common cures, and who knows how many non-common cures. It's a shame that GM hasn't provided a decision tree to help diagnose the problem. Without some guidance, we are left to our own imperfect devices to diagnose and fix the problem.

You wrote," dont get the message until i step on the brake pedal and release, and lately it has only been under heavy pressure, if i just tap on the brakes with a trailer hooked up they work fine. " That sure sounds like a brake light switch problem, and you said you replaced that. Did you use a ACDELCO switch" If not, i would invest in one. Many things for our trucks just don't work correctly with aftermarket parts. And I would lube my brake pedal pivot point so that the brake pedal goes all the way back to the top on release. I even pulled my pin out and greased it and turned it so that the wear marks were in a different position. Not at all sure it helped, but, along with other things I tried, I haven't had the problem in many years.

And the big elephant in the room, so to speak, is the TBCM itself, right next to the relay. You might get a wiring diagram of the two, to help you understand how these things work together. If you replace the module with new, it needs programming.

Personally, I think it's worth extra effort to have a reliably working antilock brake system, specially if you pull a trailer of any sort.
I’m thinking the TBCM could be it. I haven’t crawled under there yet, but found another post with the same error on a newer truck and they had major corrosion in the plug on the TBCM. I’ll take a look at that this afternoon.
 

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I'm having the issue with my 2013 where my right rear wheel speed sensor cracked In a bad snow storm and that of course sent all the traction control light, abs, stabilitrak, and for some reason set off the service trailer brake system light too? Anyone else have this issue. Confused me a little how the trailer brake message came up with the wheel speed sensor being broken?
 

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If your ABS fails for any reason, such as a bad wheel speed sensor, the truck no longer has antilock brakes and the trailer brake system fails to work. Fix the ABS system and the STBS message goes away without need to do anything else.
 

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Check the socket behind the bumper to the 7 pin trailer connector for moisture. Water intrusion in the socket can cause this problem as well.
 

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So I put the new speed sensor in. Cleaned the plug, clean the hole in the hub where the sensor goes, reassembled it. Light hasn't turned off for anything. Tried cleaning it with a scanner, nothin, tried unplugging the batteries, nothin. Another guy is having this exact same issue with a 2017 2500 gas, all the same lights on and he replaced the same sensor. Anyone know?
 

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I chased the phantom service messages for a couple of months until I ran my truck through a car wash with an under carriage sprayer. As soon as the rear was being washed the message popped up. Pulled the connection apart and sealed it with dielectric grease, and 4-1 heat shrink. No problem since.

You could also check the ground connections for corrosion. There are several, the typical failure point is the connection on the front left cab support under the drivers side door.
 

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Ya know...........Ya beat me to this same suggestion by 7 hours!

Do all the following, TBCM, BCM, 7 pin connector, Brake Light switch.

One question, have you replaced your Hydroboost? If so, and you used the newer 1011 model and did not ream out the hole in the rod that could also cause this sort of thing.

One problem for us wanting to help though is we are shooting in the dark in some respects is because we have no idea if your truck was manufactured in 2001, 2020 or where in between.

The first part of this thread will help you help us, read it.

 

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theres a link in my sig to it but when i was replacing the hubs on my vehicle... I was sent the wrong wheel speed sensor. I received an LBZ instead of an LMM. I kept getting the trailer error just as you. I went as far as to buy the new relay but that didnt work. Forgot where but i learned that speed sensor might be the cause. Well i remembered mine not looking the same. The sheathing was different. So i contacted the vendor and they confirm wrong one. Sent me correct one free of charge and all my trailer errors stopped.
 

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Ya know...........Ya beat me to this same suggestion by 7 hours!

Do all the following, TBCM, BCM, 7 pin connector, Brake Light switch.

One question, have you replaced your Hydroboost? If so, and you used the newer 1011 model and did not ream out the hole in the rod that could also cause this sort of thing.

One problem for us wanting to help though is we are shooting in the dark in some respects is because we have no idea if your truck was manufactured in 2001, 2020 or where in between.

The first part of this thread will help you help us, read it.

A few comments up I have the year of my truck. It's a 2013. I cleaned the hole where the sensor goes in, cleaned the plug and di electric greased it and still the code is coming for abs, traction control, stabilitrak and trailer braking system. The stabilitrak initializing message comes up once in a while now. But the lights stay on. My truck has always been oil sprayed and has barely any rust. I've tried checking connections and everything.
 

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Please get your computer scanned for codes, with a code reader that will interpret 'C' codes. OReilly Auto uses Bosch scanners that work just fine. If your ABS light is on, you will have problems with your trailer brake system and stabilitrak (for 4wd trucks). You need to address the ABS problem and the 1st step is reading for codes, not changing a part that is not proven to be defective.
 

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Please get your computer scanned for codes, with a code reader that will interpret 'C' codes. OReilly Auto uses Bosch scanners that work just fine. If your ABS light is on, you will have problems with your trailer brake system and stabilitrak (for 4wd trucks). You need to address the ABS problem and the 1st step is reading for codes, not changing a part that is not proven to be defective.
I originally scanned it at a chev dealer and they said the wheel speed sensor so I replaced the one it came up as.
 

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So you replaced the wheel speed sensor that the dealer identified as 'bad'? And your ABS light in the dash is still on?? If it is, you still have a problem with the ABS system and your trailer brakes REQUIRE a working ABS system to function. Perhaps you have a wiring problem on the circuit where you replaced the WSS. One of the wires is 12V, the other is the signal returning. If yo don't have 12V coming, your signal will be incorrect.
 
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