98 c3500 park brake light on

[Scupper]

Hey guys,

I think I may have inadvertently trigger a brake code on my 98. I was bleeding the master on the truck and after doing so, the park brake light is constantly on. I tried using my OBD2 scanner, but I don't think it has brake code reading capability. Already tried messing with the parking brake. Pulling up doesn't make the light go out. The light wasn't on prior. Anyways to "reset" the truck to make the light go away?

Thanks

 

[Cadillacmak]

Is that the combo parking and warning light? I cant remember all the different styles and what year did what, but I have had proportioning valves that didn't like the brakes being bled and I would have to reset them every time. They trigger the brake warning light.

 

[Schurkey]

THREE reasons for the BRAKE light on the dash to be lit.

1. Park brake switch closed,
2. Safety switch on combination valve closed due to hydraulic pressure imbalance, and
3. ABS problems.

Take the electrical connector off of the park brake switch...does the light go out? If not, take the electrical connector off of the Safety Switch. Does the light go out? If not, you've got ABS problems.

 

[Scupper]

THREE reasons for the BRAKE light on the dash to be lit.

1. Park brake switch closed,
2. Safety switch on combination valve closed due to hydraulic pressure imbalance, and
3. ABS problems.

Take the electrical connector off of the park brake switch...does the light go out? If not, take the electrical connector off of the Safety Switch. Does the light go out? If not, you've got ABS problems.

Yeah, it goes out if I unplug the ABS module.

 

[Scupper]

Is that the combo parking and warning light? I cant remember all the different styles and what year did what, but I have had proportioning valves that didn't like the brakes being bled and I would have to reset them every time. They trigger the brake warning light.

Yeah it is, I think my ABS unit is bad. I swear I can hear it sucking air as I have my helper press and depress the brakes

 

[Schurkey]

Bleed the ABS using a scan tool and the instructions attached, see what happens.

 

[Scupper]

Bleed the ABS using a scan tool and the instructions attached, see what happens.

I've read a lot of the material you have posted on the forum, but I can't seem to figure out what may help me. I can't get the rears to bleed at all. I've tried cracking the rear brake line at the module with no luck. My brake light goes out if I unplug what ever sensor it is at the valve, so I think it may be closing off the rears? Is there any literature on how to recenter? I know you said it shouldn't cut off the rears in a few post, but I'm getting no fluid at all at the rear when having my helper pump the brakes.

Edit: and yes I have bled the abs module with a Svan tool

 

[Schurkey]

IF (big IF) the Safety Switch shuttle valve is actually blocking fluid to the rear brakes, you could open a front bleeder screw, step on the brake pedal, close the bleeder screw, and release the brake pedal. That "should" move the shuttle valve and hopefully re-center it. But at that point, if the brake light is still on, you don't know which position the shuttle valve is in--too far to the rear, or too far to the front. Guys go nuts bleeding the rear, the the front, then the rear...on and on...trying to get the shuttle valve centered, and maybe going too far or not far enough. The only shuttle valves that I've worked on that wouldn't self-center were on Ford cars.

Might be useful to remove the safety switch, so you can SEE the shuttle valve position.

I have never had the shuttle valve block fluid flow, though. I hear about it occasionally, but it's never happened to me. I still kinda doubt that the shuttle valve CAN block the fluid flow...but I've been wrong before.

 

[Scupper]

IF (big IF) the Safety Switch shuttle valve is actually blocking fluid to the rear brakes, you could open a front bleeder screw, step on the brake pedal, close the bleeder screw, and release the brake pedal. That "should" move the shuttle valve and hopefully re-center it. But at that point, if the brake light is still on, you don't know which position the shuttle valve is in--too far to the rear, or too far to the front. Guys go nuts bleeding the rear, the the front, then the rear...on and on...trying to get the shuttle valve centered, and maybe going too far or not far enough. The only shuttle valves that I've worked on that wouldn't self-center were on Ford cars.

Might be useful to remove the safety switch, so you can SEE the shuttle valve position.

I have never had the shuttle valve block fluid flow, though. I hear about it occasionally, but it's never happened to me. I still kinda doubt that the shuttle valve CAN block the fluid flow...but I've been wrong before.

I gave up. I took the switch out and from what I can see with my boroscope, it looks like it is centered? The switch isn't stuck either. I just bought a junk yard module for 40 bucks. I have a feeling something is up with the valve on this one.

 

[Scupper]

Took the switch out the old one is it was absolutely stuck, plugging the rears. There seems to be a bit of debris in this one. I was able to center it back with a bit of force but I already swapped the abs body with the other one I got. I can bleed the rears now.