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Old 11-18-2018, 08:19 PM   #1 (permalink)
ucf_motorcycle
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Problem with ITBC trailer brake controller please help

On my 2014 GMC Sierra 2500 I am having trouble with the integrated trailer brake controller (ITBC).

The truck is not throwing any codes, simply the trailer brakes are not putting out anything. As if the trailer is not connected. With the wiring connected, whether stepping on the brake pedal or squeezing the lever on the ITBC controller I get no output and brakes don't engage. All trailer lights work no problem just the brakes are giving me a headache. And they used to work before on this exact trailer.

I so far have checked all the fuses, the ITBC fuse extra carefully. When I pull the ITBC fuse I do get a code but then put it back it goes away.


I also replaced the trailer brake relay thinking that must be it GM part 20904439. The one above the spare tire.


Before anyone jumps to conclusions that its the trailer (yes I thought so too). I tried two different trailers and my friends truck brakes worked but mine would not show any output at all.


I checked the wire harness on the ITBC module next to the relay and cleaned all the connections. I also checked continuity between the blue wire coming off the relay to the plug on the bumper. Everything looked in order. And no codes being thrown is what really perplexing.

Not sure where else to look at this point. Just frustrated. Every thing I have thus far found online was related to the fuses, relay and having an error message on the dash. I have non of this.

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Last edited by OkDually; 11-18-2018 at 08:29 PM. Reason: prefix/sig
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Old 11-18-2018, 08:58 PM   #2 (permalink)
johnH123
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Does it give the 'trailer connected' message on the DIC?

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Old 11-18-2018, 10:09 PM   #3 (permalink)
97chevor
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try changing the 30 amp stud 2 fuse?
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Old 11-19-2018, 01:19 PM   #4 (permalink)
Ron Nielson
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1st things first, you must have a TRAILER CONNECTED' message before ItBC will work. Also, no ABS light on the instrument panel. If either of these are problem, no trailer brakes.



It the message you receive says SERVICE TRAILER BRAKE SYSTEM, the problem is in the truck, not the trailer, 95% or more certain.



One problem area is the brake stoplight switch. If doesn't understand that you are stepping on the brakes (based on the brake switch), ITBC will produce no braking. Another problem area, on my 2008 model, there is a brake pressure sensor on the engine side of the master cylinder. This device determines how much brake pedal pressure is being applied and passes that info along the the ITBC system. Newer trucks have a similar device, but not located on the MC, to achieve similar results. I don't recall the device name or location. Perhaps others know and will post the necessary information. Or you can look for a post by heymccall that talks about this.



Some have reported that the wiring on the back of the ITBC panel on the lower dash was loose and just removing and replacing those connnections solved their issue. If nothing else, check to see if you ae getting voltage at this control unit. If you have power here, and the voltage changes with the slider, check continuity from the switch to the trailer 7-way receptacle at receptacle at the back of the truck. Also, check and clean the connection from the wiring harness to the 7-way receptacle at the back. Check wiring into the ITBC relay that you replaced and out of the relay into the ITBC module and then out of the module to the wiring harness for the 7-way receptacle.
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Old 11-19-2018, 02:46 PM   #5 (permalink)
georam1
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I'm having a similar problem. Except that mine works with the outlet on the bumper but doesn't work with the one in the bed of the truck. I've changed the receptacle in the truck bed but still doesn't work the brakes. The lights and other things work just the brakes won't. Going to replace the trailer brake wire to where it is spliced in behind the bumper next to see if that fixes it.
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Old 11-19-2018, 04:08 PM   #6 (permalink)
Ron Nielson
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The 'good kind' of bed plug has a connector to plug into the existing wiring bundle at the back of the truck, no splicing at all. The 'other kind' is a cut and splice type of a thing that often doesn't work out so well. I think I know which kind you have in your bed. I did, too, until I replaced it with the 'good kind'.
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Old 11-19-2018, 04:22 PM   #7 (permalink)
georam1
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This truck is new to me so I'm going to have to get under it and see what I have. I certainly like plugging something up as opposed to cut, splice and tape. lol
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Old 11-19-2018, 06:14 PM   #8 (permalink)
ucf_motorcycle
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No I do not get a "Trailer Connected" message. And I believe that I used to but this electric brake hasn't worked for a while now and I don't remember that until now.

I didn't use it much before but now that I need it its not working so trying to troubleshoot.

So that is the problem it isn't sensing the trailer connected. As said before I do not have any error messages at all.


Also I checked all fuses included the "stud 2" fuse and they tested good.

Not sure where else to look at this point. I can check the power on the actual ITBC control on the dash tommorow and see if its getting power. I think it is because I can adjust the range of braking on the screen.
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Old 11-19-2018, 10:00 PM   #9 (permalink)
Ron Nielson
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Your trailer has electric brakes, not electric over hydraulic??



LOTS of good information on Dieselplace about testing to see why you don't get trailer connected message by heymccall. Search and you will find. System is looking for specific range of resistance on the braking circuit of the trailer; if not detected, no trailer connected message. Some trucks more sensitive to this than others.
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Last edited by Ron Nielson; 11-19-2018 at 10:13 PM.
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Old 11-19-2018, 10:30 PM   #10 (permalink)
heymccall
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Ohm meter between blue and white wires on trailer plug (5 & 7 oclock).
Convey the reading here (should be between 1 & 2.3 ohm).

As for working on another truck, was it ITBC equipped?

And, as stated before, is the Stud fuse (30 or 40 amp) fuse still good? It is more square and has a clear lid.

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