ABS/Brake Light issues. Please help!

[rotohead]

I've been fighting a abs/brake light issue for awhile now. When I first start the truck I will get a momentary flash of the brake light, then all is fine until I drive for about 5 miles or more, apply the brakes and both lights come on. I can clear the lights by restarting the truck and drive another 5-6 miles and the same thing. First brake press the pedal seems to travel slightly further then the second or third, etc.
Here's what I've done to try to fix it. Replaced the rear diff sensor, replaced brake master cylinder (twice), replaced combination/differential valve, replaced the brake switch under the dash, had the abs module repaired by shop in Austin, TX. I've bench bled the BMC's four or five times now, also rigged up long clear hose from rear and front calipers into the bmc and used the brake pedal to bleed. I can't see any air in this system.
The front hubs are not that old, maybe six years. 2-3 year old front rotors and pads. Seems odd that it takes driving a few miles down the road before the lights are triggered. If I apply the brakes every half mile or so they won't come on. When the lights are off the ABS system works. When the lights are on it doesn't.
I'd appreciate any thoughts on this. I hate driving around with those lights on and no abs. Only other thing I can think to do is replace the two front sensors, rotors, calipers and pads. I sure don't want to do that if I don't have to since they are only 2-3 years old. TIA

 

[DavidC]

Had an issue on mine years ago. When I would reach 40mph the brake/ABS lights would come on and not extinguish unless I performed a restart. During the trouble shooting I unplugged the 7 pin trailer plug and went for a drive.............. no lights came on. I cleaned both sides with a stiff brush then packed both with Dielectric grease. Haven't had a problem again and that was at least 10 years ago.

Dave

 

[rotohead]

Thanks for that. I assume you're talking about the plug at the bumper? I just tried that and no luck for me. I was hoping that would fix it since my troubles started right around a recent camping trip where I plugged my trailer in for the first time in a few years.

 

[DavidC]

Thanks for that. I assume you're talking about the plug at the bumper? I just tried that and no luck for me. I was hoping that would fix it since my troubles started right around a recent camping trip where I plugged my trailer in for the first time in a few years.

Yes that is the one. I believe there is also some plugs either close to or behind the drivers wheel well area and can be seen looking up in that area right in front of the drivers door. If your speedo works that rules out the sensor at the rear end. Since it seems to happen as you describe the controller sounds suspect as a front sensor or wiring to those would seem to give a different problem to me. Maybe a wiring issue to the trailer plug ?. That would only be determined by finding the associated wheel well plug mentioned earlier.

Dave

 

[DavidC]

Noting the reference to the brake pedal movement I see there is also a pressure switch in the system which may be triggering the fault whether a switch problem or actual brake problem. Possibly air in the system where the pressure switch is located ?.

Dave

 

[rotohead]

Yes that is the one. I believe there is also some plugs either close to or behind the drivers wheel well area and can be seen looking up in that area right in front of the drivers door. If your speedo works that rules out the sensor at the rear end. Since it seems to happen as you describe the controller sounds suspect as a front sensor or wiring to those would seem to give a different problem to me. Maybe a wiring issue to the trailer plug ?. That would only be determined by finding the associated wheel well plug mentioned earlier.

Dave

Found that plug in the RF wheel well and that didn't do anything either.
I sent the controller into a shop in Austin, TX that repairs the module. Not much communication from them but got it back (supposedly repaired) and that didn't fix the problem. Since the abs module is coded with your vin # and it's a discontinued part from Chrysler that aren't a lot of options other then that shop and one in Chicago. In the FSM it mentions a procedure to bleed air from the ABS valve body but need to use a DRB III. I guess that's the next step. I've read on TDR that isn't necessary but I'm running out of ideas. Thanks again. The trailer plug was worth a try and would've been great if it had worked. Not my luck.

 

[rotohead]

Noting the reference to the brake pedal movement I see there is also a pressure switch in the system which may be triggering the fault whether a switch problem or actual brake problem. Possibly air in the system where the pressure switch is located ?.

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Dave

There is a combination/differential switch that mounts on the drivers side fender right next to the abs module. It is in line between the master brake cylinder and abs module. I've replaced that and its basically a sliding valve with a sensor switch in the middle. Brake lines to the front go in and out one side of the valve and lines to the rear go in/out the other. There is a bleed button on top of the valve and using my Motive pressure bleeder system I've released air from it until I get solid fluid. I'll look at it closer.

 

[B.G. Smith]

Make sure the rear brake shoes are adjusted up good and close. If they are too loose that could set the differential pressure switch. bg

 

[Road Dog]

If the brake/abs lights turn on then the correct scan tool can read the codes from the ABS module. I don't have a list of codes handy but there's a lot of rules for each code. I assume you have the basic rear wheel anti-lock brakes and probably have a Kelsey-Hayes ABS module. This article may give some insight into your problem.

 

[whistle]

With boat in tow, I was going downhill at 3-4mph, and I stomped hard on the brakes to try to get the boat to slide forward on the trailer. The ABS & brake lights came on and haven't been off since. (This happened 3 months ago.) I assume something needs to be reset, but I haven't taken it in to get the codes read (and probably won't). Brakes work fine, but I assume the ABS won't work. This is a '98 12-valve extended cab.

 

[B.G. Smith]

Your truck has discs in front and drums in rear, if the rear brakes are not adjusted up pretty good some times if you apply the brakes very fast it will set the differential pressure valve located beneath the master cylinder. I don't know if it resets automatically or not but you can view it and if the little plunger is sticking out on the end then it needs to be reset, it will have a wire plugged into it. Unless the truck was ordered with rear abs it may not have rear wheel abs. 99 was first year for all wheel standard abs. bg

 

[petersonj]

First brake press the pedal seems to travel slightly further then the second or third, etc.

For clarification - are you still seeing two warning lights on the dash? Is one is an amber ABS warning light and the other a red "Brake" warning light? If this is so, the red warning light should be addressed first as this is an indication of a significant hydraulic pressure differential between front and rear axle. A pressure differential switch will be tripped and I believe both warning lights will be set because the ABS cannot work properly if there is something wrong with the foundation brakes.

Make sure the rear brake shoes are adjusted up good and close. If they are too loose that could set the differential pressure switch. bg

I agree and this would be my first step in troubleshooting. My second step would be to remove the rear drums and inspect the foundation brakes to make sure that something is not causing the wheel cylinder pistons to travel farther than they should.

- John

 

[GAmes]

I had an ABS light & red brake light that came on , but only when the brake controller was plugged in. So I blamed the controller, bought a new one, same problem. The next step was to open the FSM and trace every wire in the ABS circuit. In the connector behind the left front wheel I found water, and a it contains the ground wire that serves both the ABS and the brake controller. With the connector cleaned and dried the lights went off, until the next time I drove in the rain. This time the lights stayed illuminated after drying out the connector. I went through the troubleshooting procedures in the FSM (have you?) and determined the ABS control module was toast. I unplugged it and the lights went out. It is still unplugged.

 

[rotohead]

I finally found the root cause of this problem. I thought I had stated my 98.5 comes stock with rear drums but I have converted the rear axle to the EGR discs. They are 1976 El Dorado (Caddy) calipers and do work well IMO but must be installed and MAINTAINED to make sure the piston is engaging properly. I've found the best way to keep that piston 'clocked' properly in the caliper is to use the parking brake regularly. It seems to push the piston different then using the brake pedal. If you don't then the piston has too much travel and will trigger the combination valve sensor and the abs/brake light. I bought a extra set of calipers on rockauto and rebuilt my old ones. I'm good to go for awhile. Anyone that is having ABS light isssues and has the EGR conversion-to-disc should look at this issue first.

 

[petersonj]

Good to know. So, even though the rear axle in your case is a disc brake system, the symptoms duplicated that of a poorly adjusted rear drum brake system. Glad you found a direct cause of the issue and thanks for posting the results.

- John