Mike in La.

Hello all, I have a 96 2500, 5.9Cummins. The abs/brake light on the dash has started coming on intermittently. It always goes off after a few minutes and the brake system seems to work fine. Reservoir is full of fluid. Anyone have any ideas? Thanks in advance for your help, I'm new to the forum and am looking forward to asking you folks alot of questions as I and this old truck age gracefully.

Mike in La.
1996 2500(150,000 miles)
2006 65hp Mahindra 4WD tractor
3 old jeeps and a ******
1 old dog, 1 old woman
Lots of guns
Lifetime NRA member

smokeyram

id look at the vacuum. My idle is all goofed up, so if im not driving with 2 feet and the idle dips, vacuum goes down, my abs and light go on. once idle goes up, lights off.

TIMMY22

If your ABS light and brake light come on, in most cases it's probably your Rear Wheel Speed Sensor (RWSS). This sensor is on top of the rear differential.

This sensor is controlled by a "exciter ring" that is interupted by the teeth on the ring sending a variable voltage signal to the computer depending on vehicle speed. small metal shavings can cause it to fail over time. The most common symptoms of the switch's failure are bad speedometer readings and tripping the RWAL computer located under the center of the dash.

Other obvious things can also trip the computer such as:

1. bad pads, shoes, calipers, wheel cylinders.

2. bad fuses.

3. poor connections or broken and/or chaffed wire.


Once you have detemined that none of the above exist, you can try a system reset buy pulling the abs fuse and/or pulling negative battery terminals for 30 sec or so.


If the lights come back, the next thing to try is reading the RWAL fault codes.

To read the codes on 96 and older trucks:

1. turn key to the "on" position.

2. for just a second, ground pin # 13 on the diagnostic plug located on the knee bolster (#13 is a black wire, it's the 4th from right bottom row).

watch your ABS/Brake light for codes.

start counting with the first long flash, end with last short flash.

there are only 13 codes.


1. Not used.
2. open isolation valve wiring or bad control module.
3. open dump valve wiring or bad contol module.
4. closed rwal switch.
5. not used 4wd. over 16 dump pulses in 2wd.
6. erratic speed sensor reading. (most common)
7. electronic control module fuse pellet open, isolation output missing, or valve wiring shorted to ground.
8. dump output missing or valve wiring shorted to ground.
9. speed sensor wire resistance/ high reading.
10. speed sensor wire resistance/ low reading.
11. brake switch always on, RWAL light comes on over 40mph.
12. not used.
13. electronic control module phase lock loop failure.
14. electronic control module program check failure.
15. electronic control module RAM falure.

mine was a code 10. it was a break in the molded section of wire off the RWSS.

*On 97-98.5 12V models, you will end up at the dealer to get the ABS codes.


Hope this helps, and good luck!

qmlogan

Most Times It Is The Rear Wheel Speed Sensor. Very Easy To Change And Not Expensive. Sometimes It Will Do Funny Things To Your Speedometer As Well (wont Register Speed Until About 20mph), But Not Always.

Cougsfan

When that happened to me, I checked the things that these guys mentioned, but eventually found that it was the stop light switch mounted near the top of the brake pedal. If you pull up on the brake pedal with your toe and it goes away, replace the switch. If not, listen to what the other guys said.

kbrashears

Well, I replaced my RWSS this evening and that wasn't it. I'm not quite sure where the diagnostic plug is. Hey, I'm learning....

kbrashears

Okay, found diagnostic plug hidden (tucked up in there). I grounded the 13 pin and.....nothing. Lights did nothing.

runningbird

humm, I'm watching this one also.

polaris800sp

i found on my truck that it was some wiring leading back to the sensor on the rear differential. the wiring was rubbed through. i replaced the sensor before i found the wiring problem so not sure what was the exact problem.

kbrashears

Okay, but if your ABS ISN'T working, then it has to be the module, right?

kbrashears

Still looking for an answer.

kbrashears

help

(I'm going to keep typing help until I get some)

I've searched high and low. Can't find a definitive answer. If your ABS doesn't work and your light is on, does it HAVE to be the module? Is there another problem? Fuses are good.

98ramcummmins

try bleeding your brakes, worked for me, cheap option

yellowrosefarm

On my 98 2500 the abs and brake light just popped on today. The speedometer is working fine. I read in the operators manual of all places that these two lights come on if the parking brake is depressed. That would jive with the RWAL code for brake light staying on too. I unplugged the connector at the parking brake and the lights went off. When I have time, I'll get into the switch and see what's up. It's a single connector so it just allows a path to ground. I'm wondering if some of y'alls intermittant problems might also be related to this switch.

fschiola

This is the next thing I would look at before I did anything else. You should also check to see if the parking brake pedal is coming all the way up like the last poster suggested.