2nd Gen Non-Engine/Transmission PB/ABS lights "on"

[MWinters]

I need some troubleshooting guidelines. I have a 99 Quad Cab w/rear ABS only. All stock. 57,000 miles. Manual transmission. My parking brake light in the dash came on yesterday, & although not at the same time, the ABS light came on soon after. I know the parking brakes are not engaged as the truck can be pushed easily by hand & it coasts when clutch is pushed in. Service brake performance seems OK.



The service manual indicates a combination valve controls these lights. It states that a pressure drop in the brake system causes the lights to come on. I don't see any way to diagnose this.



I tried disconnecting the wire to the pressure differential switch , but this did not help. I've also disconected all power, & this also did not help.



Would bleeding the brakes re-set this system ? I don't think there is anything drastically wrong, but I've been wrong before !!!



Any thoughts ?



Thanks for listening



Hot Rod Mike.

 

[Midnight]

Mike,chances are it's your speed sensor located in the top of the diff. This is a very common problem. If you don't have access to a scanner you may have to just replace it and hope for the best.

 

[Mike97TJ]

I would bet its the speedsensor on the rear diff. I had to change mine monday. It was only 30. 00 at local dealer. They told me they sell 4-5 of these a day.

 

[nwinters]

My truck has 140k plus on it, I had the same problem at about 120k All mine needed was a good cleaning. I put it back in and haven't had trouble since.



Nate

 

[emjay]

Sounds like a lot of people have had that problem and found the solution, but here's my $0. 02 FWIW:



In the old days a differential pressure switch was used between the two brake circuits on dual master cylinder brake systems. If one circuit had hydraulic pressure (i. e. rear brakes) and the other (i. e. front brakes) had low or no pressure, the valve in the switch would move from one side to the other, switching on the brake lamp on the dash. In theory, once the pressure differential was located and repaired (usually the master, unless you're leaking a bunch of fluid), you could reset the switch by applying pressure to the failed side.



Fast forward to today's systems, I'm guessing that possibly the action of the switch could have set a code in OBD, which would explain the inability to extinguish the light by disconnecting the pressure switch. Anyway, hope this helps.

 

[GotDodge]

Just had the same problem two weeks ago. Toke it out and cleaned it. Reset the computer. No more lights in dash.

 

[TWhiteside]

I have a 99 QC 4X4 Manual with RWAL with 65000 miles and had the same thing happen this weekend. Besides the ABS and Brake Lights, the speedometer would not work below 20MPH. I took out the sensor and cleaned it, but that did not work. So I replaced the sensor and all is fixed.

 

[Henry]

speed sensor

Speed sensor on rear diff. I had same prob and dealer relaced it under warranty.

 

[MWinters]

lights on follow up - Part 2

OK guys, thanks for the quick & informative responses, but... .



I crawled under my truck as soon as I got home today, & after 15 minutes or so (OK, more like 45 minutes ) I got the speed sensor out & cleaned it up. Reinstalled same sensor & did not solve the problem.



So do I gamble & replace it, hoping for the best ? If I take it to a Dodge dealer, & they plug in their diagnostics for troubleshooting the system, what does this cost ? Also, since this plans to be the truck that takes me to the graveyard, I might be interested in getting some of my own diagnostic equipment. Is there anything out there that is reasonably priced that covers all systems ? Or do I spend $ 100 or so & get something that is restricted to just a few systems? I've never seen any of these scanners, so I'm in the dark on these things.



Hey "GotDodge" - you mentioned resetting the computer - how do you do this ?



Thanks to all for the help. Its really apreciated.



Hot Rod Mike



P. S. Hey Nate - are you my long lost brother ? Are you extremely handsome, charismatic & just the life of the party ? Well, then you're probably NOT related to me !!!!

 

[sbiel]

My 98. 5 5 speed 4wd w/4 wheel ABS lights up both the ABS and brake light. Tried replacing the sensor and the problem has been REDUCED, but not eliminated.



How does one go about looking cracked wiring and other possible issues ??



thanks, steve

 

[GotDodge]

MWinters

To reset the computer unhook the batterys for 30 sec.

 

[emjay]

You can also unplug the three connectors from the PCM for 30 sec or so, which is easier IMHO.