At a loss service brake system

[Doubeleive]

Ok first off this is a 03 2wd 1500 Silverado, I'm posting in here because the sister site is super slow for some reason and system is essentially the same, I changed the front pads this morning, all I did was c clamp the calipers install new pads, put wheels back on, started it up pumped the pedal a few times and now I have the service brake system message, no abs light. Connected tech2 and it shows no dtc of any kind anywhere, so I'm lost, fluid was not low but I added about 6oz just to see, no change, any ideas? Doesn't seem like it would be the abs module.

 

[Doubeleive]

Unplugged this harness message is gone while unplugged

 

[Doubeleive]

so.. I'm guessing the proportioning valve is stuck

 

[Doubeleive]

on a positive note the truck didn't have a single DTC of any kind, I guess that's a good thing, lol

 

[swathdiver]

What about the setting that says Diff Pressure Fluid Level Low and the ABS Relay Command ON?

 

[Doubeleive]

What about the setting that says Diff Pressure Fluid Level Low and the ABS Relay Command ON?

I don't know, and I don't know if that is normal or not I guess I will find out when the valve is replaced or corrected. I couldn't get beyond that point I could select it but there was no other option beyond that, the abs light is not on and there is no code, brakes work fine but I am sure the valve is stuck and cutting fluid flow to the rear brakes, the valve has a centering V spot where the switch sits (normally) so if the valve is forced forward or backwards it contacts the switch and causes the brake light to come on. It might be able to be corrected by bleeding the lines at the valve but I am not sure on the success rate of that it was to late today to ask the dealer or another shop I will have to wait till Monday unless someone else chimes in that has experienced this problem before. doing a little research on the valve only led me to determine that it is indeed the problem given there is no air in the lines, no abs codes, and when I disconnect the switch the brake light goes out and error in the dic goes away, tried banging it with a hammer, tried pressing the brake pedal as hard as possible, tried slamming on the brakes, nothing seems to be getting it unstuck. the brake fluid looks nasty the whole system needs to be bled so it's just matter of if the valve can be corrected or if I should just order one they run about $100 online.

 

[Doubeleive]

I think I caused it to happen somehow I put the wheels back on, dropped the jack and started it up and forgot to pump the brakes before I put in gear and I started rolling towards the Denali and I slammed the brake pedal to the floor and that's probably when it jammed the valve and the error popped up.

 

[swathdiver]

Is there a way to test the valve in one of the other menus in the Tech2?

 

[Doubeleive]

Is there a way to test the valve in one of the other menus in the Tech2?

not that I could find, the valve is mechanical and the sensor is either open or closed, I guess I could leave it unplugged and run the tech2 on it and see if any of the readings come up different. I kind of found it by accident because I was checking to see if it was a faulty low fluid sensor but this truck doesn't even have a brake fluid level sensor, it has a spot on the tank for one to clip in but no harness.

 

[Doubeleive]

I tested it again with the harness off and the diff pressure changed to ok and brake light command off otherwise everything else is the same, so even though it doesn't give a DTC it does indicate what the sensor reads

 

[swathdiver]

So the sensor is bad then? I'm a little slow to understand, sorry.

 

[fire730]

I would go find a gravel / wet road in a safe area and jam the brakes a few times to cycle the system. Make the abs system work. I would do that before I started throwing parts at the truck.

 

[Doubeleive]

So the sensor is bad then? I'm a little slow to understand, sorry.

the valve is jammed, the sensor is working.
the valve distributes the brake pressure to all 4 calipers (basically front or rear), it is a safety valve that is designed to prevent brake failure, so lets say I blew the left front brake line, the valve would move and direct brake pressure more to the back brakes so I could still stop safely. when it moves it then touches the sensor and sets a error.

 

[Doubeleive]

I would go find a gravel / wet road in a safe area and jam the brakes a few times to cycle the system. Make the abs system work. I would do that before I started throwing parts at the truck.

ya I gave it a few slams and bangs it's stuck, it needs the whole system cleaned out anyway so going to see about it tomorrow I don't have any helper (other than a 6yr old) or a bleeder setup

 

[Rocket Man]

Betcha about crapped your pants when the pedal went to the floor as you were headed toward the Denali!

 

[Doubeleive]

Betcha about crapped your pants when the pedal went to the floor as you were headed toward the Denali!

yessir! sudden realization I ****** up, lol I am pretty sure that's when the valve stuck (panic pedal)

 

[Doubeleive]

Is there a way to test the valve in one of the other menus in the Tech2?

I doubt it since it is a mechanical valve, I could unscrew the sensor but not sure if that would introduce air into the system or not

 

[swathdiver]

the valve is jammed, the sensor is working.
the valve distributes the brake pressure to all 4 calipers (basically front or rear), it is a safety valve that is designed to prevent brake failure, so lets say I blew the left front brake line, the valve would move and direct brake pressure more to the back brakes so I could still stop safely. when it moves it then touches the sensor and sets a error.

Oh OK, when I was a kid that part was called the proportioning valve and it was mounted on the frame under the driver on my old Buick. I had to replace the one in my '79 once.

 

[Doubeleive]

Oh OK, when I was a kid that part was called the proportioning valve and it was mounted on the frame under the driver on my old Buick. I had to replace the one in my '79 once.

the test from what I gathered is to just unplug it, you can test it with a lighted probe to see if moves back to the correct position when bleeding the lines or it may make a pop sound when going back into the correct position from what I was reading. another thing that makes me pretty sure that it's stuck is the sensor is basically saying "low pressure" with just the key on, if it was the master cylinder or something else I would think it would only say low pressure if the engine was running and vacuum was present.

 

[02Lightning]

I’ll bet you can force that valve the other direction, by opening the opposite side of the system and pushing the brakes to the floor with a rear bleeder open. Closing it of course before letting the pedal up.