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I need some help guys..... Ok I have done a exhausting search of this topic but I still need a little help. I have the truck in my sig below. I only have 10000 miles and for the first time hooked up my travel trailer. Everything worked perfectly. After I unhooked the trailer I got a service trailer brake system on my DIC. No other lights. My brakes work fine and no ABS light. I have tried cleaning my plug connectors, including the fifth wheel plug. I found the brake controller box up on the frame behind the rear wheel on the driver side. I disconnected it and blew with a air compressor. I still get my message on DIC. I have read about a ground issue but couldn't find anything on the forum where the ground connector is located to check to see if this is the problem.

I also tried to hook back up my trailer to see if this would clear it. Now my trailer works (lights and brake and turn signals) but my brakes won't work. I get a trailer connected but no brakes. Is there something I can do to fix it, as I do have mods on my truck and I don't want to fight the dealer about oversize tires make the service trailer brake light come on, especially since the truck has been lifted almost 3 years ago when bought new. Thanks for any help you van provide.
 

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I have the same problem. I hve searched and searched but you are the first to post the exact thing mine is doing. I am trying to get off work tomorrow so I can take it to the dealer.
 

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Dealer looked at mine today, said it was the pressure sensor or something that reads hydraulic pressure from the master cylinder. I'll know more tomorrow when I pick it up and have the parts list in front of me.
 

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Discussion Starter #5
Dealer looked at mine today, said it was the pressure sensor or something that reads hydraulic pressure from the master cylinder. I'll know more tomorrow when I pick it up and have the parts list in front of me.[/QUOTE


Took mime to the dealer today. I couldn't find the problem myself. It was the same thing..... The pressure switch on the hydroboost. It's fix for now.....
 

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I had that happen once, but it went away on it's own. Nice to know what is the cause. BTW the link above doesn't work.
 

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I've noticed on mine if the truck is running and you:

-plug the trailer in, all the trailer lights will work but the brakes won't activate
-unplug the trailer, I'll get the service trailer brakes message on the DIC

I make sure to turn the truck off now whether connecting or disconnecting my TT..
 

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Same problem here. Service Trailer Brake message. Lights work (slide in and trailer) but no trailer brakes. Sooo, does anyone have the part number for the pressure switch? Thanks!
 

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Actually, I doubt my problem is the brake pressure switch as I get the Service Trailer Brake message when I turn on the ignition (even if I don't actually crank the engine). Tried to see if I threw any codes using my cheapy ODB2 reader, but no codes visible. My guess is its the actual module. That's a $400 part from my local dealer. Other than disconnecting it and going with an aftermarket unit, or spending that kind of $ on a factory unit, any thoughts? All fuses are good. The above link regarding testing the system does not work. Thanks!
 

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Well, regardless, the brake pressure sensor part number is 15838718 in case anyone needs it.
 

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Well shave my butt and call me purdy. Swapped out the brake pressure sensor and bingo! Problem solved. Got the part from Discount GM Parts (Flow Chev). Best $80 or so I ever spent.
 

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Dealer looked at mine today, said it was the pressure sensor or something that reads hydraulic pressure from the master cylinder. I'll know more tomorrow when I pick it up and have the parts list in front of me.

Took mime to the dealer today. I couldn't find the problem myself. It was the same thing..... The pressure switch on the hydroboost. It's fix for now.....

Are you still fixed? Any more problems show up after replacing the brake pressure sensor? And was it raining or wet outside when you would see this ITBC problem?
 

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same problem same fix

My '08 GMC 2500 Duramax has had the same problem for over a year. I haven't had the need to tow so I basically ignored it. Seeing how the truck is
almost off warranty I went by the dealer and they said that switch was bad on the master cylinder and replaced it, then power bled the front brakes.
The sensor converts the pressure to a voltage output to the trailer brake control to tell it how much to brake. Mine was zero all the time on output since it was dead. All fine now.
 

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Mine is doing the same thing. Does anyone have any pictures on how to replace the sensor, or how to test and make sure that is what is bad?
 

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It's pretty simple. Unplug the sensor, unscrew it, replace it and make sure you put in a new o-ring. Do not lubricate o-ring or sensor. Plug in sensor. Bleed brakes front wheels only.

Lots of people who have problems with their ITBC find that this is the fix for their problems. And the sensor price is pretty reasonable if you shop around.

If you hook your trailer to your truck and the DIC says TRAILER CONNECTED, step on the brakes and the DIC display should show more 'blocks' as you increase the pressure; less blocks as you lighten the brake pedal. If you don't see the 'blocks' increase as you increase pressure, it's likely the sensor.

 

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is there any way to test the sensor before removing it or buying a new one?
 

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I've read your other posts, I know its not a trailer issue. I was wondering how to figure out how to troubleshoot the sensor that some seem to have had luck with replacing.
 

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I've read your other posts, I know its not a trailer issue. I was wondering how to figure out how to troubleshoot the sensor that some seem to have had luck with replacing.
I'm gonna assume that you made a tester for the ITBC output (if you didn't, quit making excuses), SO...........

The Master Cylinder Pressure Sensor operates from a 5V reference generated within the EBCM. It also has a ground and an output.

Pin A (Ye/Bk tracer)....... Ground (referenced, not chassis)
Pin B (Gray)..................5 Volt reference
Pin C (Orange)..............Sensor output

With the pedal not depressed, key on, measure across B to A with a digital voltmeter. Voltage should be around 1 volt. Have a helper depress, slowly, the brake pedal all the way to full apply, and the voltage should rise to nearly 5 volts. Failure to change voltage will indicate a faulty sensor.


BTW, resistance between the blue and white wires on the trailer must be 2.0 Ohms or less. One magnet will not allow the system to operate under pedal braking BUT it will respond to the manual apply.
 

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I'm gonna assume that you made a tester for the ITBC output (if you didn't, quit making excuses), SO............
Ha ha. yes, I have followed alot of your previous posts. I always check on here before I ask. I have measured ohms on the trailer and it is showing fine.

I tested my plug with your tester, made it free with parts lying around.

I have been reading other posts of issues people have been having and many trips to dealers changing controllers and relays, and anti-lock brake sensors.

This sensor sounds like it might be easy and cheap enough to try first. But i wanted to know if there was a way to test it.

Thanks for all your help. I have learned so much more on trailer brakes and controllers from your posts.
 
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