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2015 2500HD "check trailer wiring" and "service trailer brake system"

i have a 2015 2500HD 6.0. it has the factory trailer brake controller and i have been getting "service trailer brake system" and "check trailer wiring" it has been to the dealer twice for this and the first time the service trailer brake system light would not go out even if it didnt have a trailer hooked to it. the first time they replace the module above the rear axle and it seemed to fix it and when i pulled a trailer a few weeks later it cmae on again saying to check trailer wiring and service trailer brake syatem. the replaced the plug and it still does it. it seems to do it nearly all the time when i have a trailer hooked to it but there has been a couple of times it acts normal. the truck only has 33k miles.
 

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On the label in the glovebox, do you see "UY2" listed?
 

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Discussion Starter #4
it has the gooseneck/5th wheel wiring prewired as an option from the factory. i have a 7 way plug mounted in the bed hooked to it. i have also took it apart and checked to see if there was any wires crossed and there wasnt. i also removed the plug and checked to see if that was the problem but it still does t with it removed
 

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i will have to look. what does that code mean?
UY2 - CAMPER/5TH WHEEL TRAILER WIRING PROVISIONS
This is additional wiring to supply circuitry to your camper/trailer. Your 7-way in-bed receptacle may or may not utilize this wiring. Depends on who installed the in-bed 7-way.

Service Trailer Brake System
means that the trailer braking system in the truck has a problem whereas the Check Trailer Wiring means that the truck has detected a fault in the trailer wiring and this is usually a very good indicator of where the problem is.

When the dealer replaced 'the module', was it the trailer brake module or the trailer brake relay? They are located next to each other on the frame above the left rear wheel. Just want to be sure what was/wasn't replaced.


 

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When you have your trailer connected and displaying the STBS message, unplug the trailer connector at the frame (see #2 in diagram). This will take that wiring harness out of the picture as far as a possible problem area. If the problem remains, you know to look elsewhere.

View attachment Trailer Connector diagram.pdf

This diagram is from my 2008 - yours may be a little different.
 

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i have a 2015 2500HD 6.0. it has the factory trailer brake controller and i have been getting "service trailer brake system" and "check trailer wiring" it has been to the dealer twice for this and the first time the service trailer brake system light would not go out even if it didnt have a trailer hooked to it. the first time they replace the module above the rear axle and it seemed to fix it and when i pulled a trailer a few weeks later it cmae on again saying to check trailer wiring and service trailer brake syatem. the replaced the plug and it still does it. it seems to do it nearly all the time when i have a trailer hooked to it but there has been a couple of times it acts normal. the truck only has 33k miles.
I was having the same problem. I would hook up to my travel trailer, no issues.

Then I would hook up to my flatbed trailer and have the same exact issues you have. This is how I fixed it:

I looked at the male end of the 7 pin connector on my trailer. The contact tabs were all flat and didn't look like a good connection could be had. I took a screwdriver, slid it in between the tabs and the connector and bent them inward a little. I haven't had an issue since.

Hope that helps.
 

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There are many places where there can be a problem causing the Service Trailer Brake System to appear on your DIC. Here are some items to check. I suggest you do 1 step at a time and see if the problem is fixed before going on to another step. It will help others to know where you found your problem, so report back what your problem/fix turned out to be.

1) Trailer Brake Relay and Module - located above the drivers rear axle on the frame, next to the Trailer Brake Module. The Relay is cheaper than the module and does not require any programming by a dealer or shop. Just replace it. Power flows thru the module to the relay, then onto the trailer braking system. If you have output from the TBM but no output from the relay, replace the relay. If no output from the module, replace the module and have it programmed. Relay is a more likely failure point. See the detailed instructions on checking module and relay circuits below.

2) Brake Pressure Sensor on the master cylinder. This sensor tells the braking system how hard you are stepping on the brakes for the truck so that it will know how to brake the trailer. If it doesn't work, your trailer brakes don't work or don't work correctly. Easy replacement - just make sure you don't deplete the brake fluid in your master cylinder when removing old and replacing with new. The BPS was later replaced with another similar device not attached to brake master cylinder about 2011/12 model year. I an not sure what this is called or the location.

3) Fuses - Sure check any fuse/relay relating to trailer functions of any kind. Also the Stud 1 & 2 fuses. They will mostly be in the under hood fuse box. Also check the Park lamp Fuse labeled INT PRK 10amp in the instrument panel fuse box. Test them with a volt meter or test light - do not just look at them.

4) Brake Stop Light Switch - many reports of these causing trailer braking problems. Cheap and easy to replace.

5) ABS system - if you have an ABS light, fix that problem and your STBS message will likely go away. You must have a working ABS system for the trailer braking system to function.

6) Center mounted stop light - this must be functioning, similar to the ABS system.

7) Blunt Cut Camper Wiring. If your truck has this option, look at the cut end (bare wire ends) of the wires and make sure they are not grounding anywhere. I coated mine with dielectric grease and covered about the last 6" of the bundle with plastic and taped it shut.

8) Other trailer wiring - Remove the connector for the trailer wiring at the rear frame cross member. This will not solve your problems, but it will eliminate problems that may be caused somewhere in this loom for troubleshooting purposes. While you have it off, clean all connections and coat with dielectric grease. Thoroughly clean your 7-way receptacle and coat with dielectic grease also. Clean the contact lugs with a small brass brush, like a .22 cal bore cleaning brush or similar.

9) Trailer Brake Module Switch - Check the wiring connections at the Trailer Brake Module Switch located on the dash- the one where you can adjust your gain. Some reports that there may be disconnected wiring here.




Circuit/System Testing
Important:
These diagnostics are based on having no trailer connected.

A simple volt meter and test light will do fine for this testing. Of course, if you happen to have a nice scope, that will make it easier or at least a more interesting device on which to review the results. It will help you enormously if you have a wiring diagram of this portion of your truck to verify terminals, wire colors, etc. Obtain wiring diagrams at BBB Industries- Premium Alternators, Starters, Power Steering Products | TSB's & Wiring Diagrams



1. Ignition OFF, disconnect the harness connector at the solid state relay.

2. Test for less than 5 of resistance between the ground circuit terminal B and ground.
If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition OFF, verify that a test lamp illuminates between the B+ circuit terminal F and ground.
If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal
and the STUD 2 fuse is open, replace the trailer brake control relay.

4. Ignition ON, verify that a test lamp does not illuminate between control circuit terminal E and ground.
If test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.

5. Ignition ON, verify that a test lamp does not illuminate between control circuit terminal E and B+.
If test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the TBCM.

6. Ignition ON, test for 3.2-4.1 V between the control circuit terminal C and ground.
If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the TBCM
If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.
7. Ignition ON, test for 3.2-4.1 V between the control circuit terminal A and ground.
If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal,
replace the TBCM.
If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.

8. Ignition ON, test for less than 1 V between the control circuit terminal D and ground.
If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.

9. If all circuits test normal, replace the trailer brake solid state relay.
replace the TBCM.
If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.
 

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I gotta wonder, Ron, if that ain't gonna be for a '15. Didn't the separate relay go away with architecture change, along with the pressure sensor?
 

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Scratching my head, Brakes were weak on 5er with factory controller. i put in a prodigy 2 controller and they were better but still weak. I never had 12v power at plug for charging trailer battery, so i run new wire from battery to plug with a breaker in there. Hooked to the 5er the controller was on max, pulled ahead slight down hill hit brakes and trailer locked up! never could even come close to that before. Took out to dealer to have work done and now i don't need it on max.HAPPY CAMPER! LOL Maybe i got better brakes cause the camper battery has more voltage? Do camper brakes run off the camper battery? I'm just curious cause i didn't think the system worked that way. Thought i would share this just in case? when it rains I'll get that DIC trailer message
 

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Scratching my head, Brakes were weak on 5er with factory controller. i put in a prodigy 2 controller and they were better but still weak. I never had 12v power at plug for charging trailer battery, so i run new wire from battery to plug with a breaker in there. Hooked to the 5er the controller was on max, pulled ahead slight down hill hit brakes and trailer locked up! never could even come close to that before. Took out to dealer to have work done and now i don't need it on max.HAPPY CAMPER! LOL Maybe i got better brakes cause the camper battery has more voltage? Do camper brakes run off the camper battery? I'm just curious cause i didn't think the system worked that way. Thought i would share this just in case? when it rains I'll get that DIC trailer message
Sounds like you have EOH brakes, and the actuator pump is running off the trailer house battery. Not a bad thing, but, as you've discovered, the hydraulic pump needs good voltage.
 

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I gotta wonder, Ron, if that ain't gonna be for a '15. Didn't the separate relay go away with architecture change, along with the pressure sensor?
I knew that there was a change (you told me about the change) but I don't have enough details to post on the board. I'm still stuck back in my 2008 truck and guessing about other years. Time does change things.
 
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