2007 GMC Sierra 2500HD brakes locking up

Dom Salvagna · August 18, 2018

I have a 2007 GMC Sierra 2500HD with brake issues. The passenger side front brakes were locking up intermittently and the truck was pulling to one side and slowing down occasionally. The brakes finally locked up completely and the caliper appeared to be stuck. I replaced the right front caliper, rotor and pads and it locked up again! I also have a message on the dash to 'service trailer brake controller system' that has been there for a while but I've been ignoring it not thinking it will affect anything. Could the trailer brake controller be causing this or could it be the ABS system? It appears to be only the one wheel so I traced the brake lines back to a module under the drivers side door which I believe is the ABS? It is hard to get to but could this be the problem? I've read some other posts with similar issues and there seems to be many possible causes. I've tried to release the pressure at the master cylinder but that doesn't work but it does unlock when I loosen the bleeder. Any suggestions?

Doug_Scott · August 18, 2018

You have an issue with the trailer brake controller that you have ignored for too long. You could try removing the fuse for the trailer brakes and see if that prevents it from keeping pressure applied on the one side of your braking. Chances are thr left rear is also being applied slightly as well.

You need to retrieve the error codes from the trailer controller system. I have no idea if they are accessed via a typical ODB2 code reader though, I have one so I would try it and see were it my vehicle, but it's not, so I can't.

Dom Salvagna · August 18, 2018

Thanks Doug. Couldn't find a fuse for the brake controller so looked it up and it appears to be stud 2 if I am correct. Pulled the fuse and it still locks up. Pulled the fuse for ABS also (there appears to be 3 fuses labelled ABS1, ABS32 and heavy duty ABS. I pulled one at a time and still locks up. Should I pull all of them? And if it is what would be the cause?

Doug_Scott · August 19, 2018

Are any other wheels getting hot? Take wrenches that fit the flex hose to steel line on frame for the right front wheel, and instead of releasing pressure at bleeder, release it at the steel line to flex hose connection. The reason I suggest this is because I have heard people say that flex hoses can become like a one way valve and hold pressure on the caliper. I have zero first hand experience on this, but maybe some of the people suggesting it have. I have seen a lot of strange things with brakes myself, just not that one. Give it a shot and see. If loosening the steel line does not release the pressure, then you likely have a bad flex line, and I will finally have a real close to first hand experience with it.

Also take the cap off the master cylinder and check out the rubber inside the cap. If it is all swollen up and spongy, that is a sure sign that someone put oil into the master cylinder instead of brake fluid.

Dom Salvagna · August 20, 2018

I had the dealer check the brake controller message a year or so ago and they said it was a computer issue and cleared it but it came back soon after. So far replaced a Trailer Towing relay that I read could have caused the Trailer Brake Controller message and it did clear. Thought I was on the right track. Pulled some fuses and checked wiring connections to the ABS. Brake still locking up. So far haven't noticed any other wheels locking up. I'll try checking the hoses next as I have read the same thing about them breaking down and creating a check valve.