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

38K views 22 replies 9 participants last post by  rotorav8r 
#1 ·
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.
 
#2 ·
On the label in the glovebox, do you see "UY2" listed?
 
#14 · (Edited)
I have the UY2 code, is there a defective part with this code? I have been chasing this error on a trailer for weeks and have replaced all the trailers brakes, magnets, and wiring. I have now replaced the 7way plug, the junction box and the emergency brake, breakaway box. I’ve also swapped the trailer brake module under the truck and the dash control inside the truck, all with no luck. It only does it on our larger trailer not out small trailer. However, the large trailer works with two other newer Ram and Ford trucks. The Chevy alarms occasionally on the smaller trailer but usually works fine on it. It works the brakes on the large trailer right when connected then errors and refuses to operate the brakes all together on the big trailer. Talk about a dangerous refusal to operate! The brakes function and work fine behind my ‘18 Ram.

Side note, my 2015 Chevy has the trailer brake module above the ABS Module, both are above the spare tire. There is no relay there or bolted to the frame. Connectors on both are real clean.

2015 Chevrolet 2500 Silverado Diesel
 
#5 ·
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.


 
#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
 
#6 ·
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.
 
#7 ·
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.
 
#9 ·
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.
 
#10 ·
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?
 
#13 ·
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.
 
#11 ·
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
 
#12 ·
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.
 
#15 ·
UY2 is basically a Tee harness that allows an in bed, additional, 7 way plug, for fifth wheel towing.
If you don't have a 2nd 7 way plug installed, disconnect the bumper plug from harness, follow harness to next matching connector, and remove the Tee harness. Then, reconnect the bumper plug to the truck harness.
 
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#16 ·
UY2 is basically a Tee harness that allows an in bed, additional, 7 way plug, for fifth wheel towing.
If you don't have a 2nd 7 way plug installed, disconnect the bumper plug from harness, follow harness to next matching connector, and remove the Tee harness. Then, reconnect the bumper plug to the truck harness.
Thank you for your reply! I’ll try that. This is my girlfriend’s truck. She recently had the Chevy dealer install the fifth wheel hitch and plug in the bed but they failed to use the staged wire for it. It is still zip tied in the rear bumper. They also have no idea what signal the truck is looking for before setting the error as far as current or resistance.
 
#17 ·
No luck so far, does anyone else have any ideas? One post said the dealer can reprogram the computer to look for other parameters (the problem I suspected all along). Has anyone heard of that? The local Chevy dealer seems dumb on this. They have no idea, they said it sounds like I know more about the trailer brake system than they do. They were not being sarcastic.
 
#19 ·
I had the Service Trailer Brake System message come up once just driving around without my trailer attached. Hasn't happened since. Weird. Trailer brakes seem to work fine.
 
#22 ·
rotorav8r - I have a 2016, I do not get the Service Trailer Break System but do get the Check Trailer Wiring. I have had mine to an independent shop (they say it is the truck), Trailer Shop (they say it is the truck) and Chevrolet (they say it is the trailer).

The message comes and goes quick (ie: disconnected/connected). It seems to happen up hill or down hill and I suspect it is grounding thru the ball. When I get the message, I loose that ground. I have looked for a bad ground but havent located it.

Let us know if you find your problem. Thks
 
#23 ·
If I figure out the issue I will let you know. I do have a ground connected from the junction box right to the trailer frame. In addition to the brakes grounding back to the harness wiring I have now also run separate grounds from each connection point right to the frame too. I’m almost wondering if the truck doesn’t like the frame grounding and that’s what disables it. Usually a lot of grounds is a good thing in my electronics and circuit board repair experience.
 
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