ABS and Brake light on all the time

[KennyM]

The ABS and Brake light came on and stayed on. My truck just crossed 70,000 miles. Do I have a possible problem? Ken

 

[Rnpeder]

If both light stay on, check your brake lights. If they are out, replace the fuse. Just one of many possibilites.

 

[DennyDay]

Lights

Check speedo - - same thing happened to my '99 when speed sensor was going out.

Denny

 

[Midnight]

Ken

The most common problem is the speed sensor. It is in the top of the diff. Un plug and check for resistance. I can not remember off the top of my head the specs tho.

 

[DarrellB]

Mine is a 99 and it is doing the same thing, had it in the dealer today for a rear pinion seal and they ordered the speed sensor. If you can wait till about Tuesday of next week I will let you know how much it cost to have fixed.



Big D

 

[KennyM]

Sounds good DarrellB. Does this sensor tell the ABS that the wheels have stopped turning or is there more to it. Ken

 

[K_Arts]

Hey guys... could this also be the infamous Clock Spring??



Kev

 

[Archive]

Is the master cylinder full?

 

[RHARVEY]

My ABS light flickered a couple of times this morning as I pulled into the parking lot at work. It has never done that before. . so we will wait and see. .



Rick

 

[KennyM]

TopFeul, The Master Cylinder is full, That was the first thing I checked. RHarvey, Mine started as a flicker to by the end of a 400 mile trip on Wed it was on all the time. On Sat I will Ohm out the sensor, it would be great to know what Resistance to look for. I will assume an open is bad. Ken

 

[DarrellB]

Kenny, not sure what it really does I think it also has a hand in the operation of the speed ometer and the cruise control. They said it would only take about 20 minutes to replace and then about anouther 5 minutes to erase the codes stored in the computer.



I have a service manual and looked at it last night and it looks like the sensor is right on top of the rear diff. in the middle of the housing. I would fix it myself but if it only takes the dealer 25 minutes I'm all for letting them do it.



I will let you know as soon as I have it done.



Later Big D

 

[KennyM]

Big D, Had my speed sensor replaced today. Cost was $ 118. 71. Thats for labor and part. Just to make note when the amber and red brake lights are on ABS is disabled.



Ken

 

[DarrellB]

Kenny, had mine done Today and it cost $78. 58 labor and parts. I had to find out the hard way that the ABS was disabled. I had a 13 point buck jump out in front of me Sunday morning at about 3:30am I stomped on the brakes and all four locked up. Had to take to the feild to avoid hitting the damn thing and then i almost got hung up in the feild.



Thanks

Big D

 

[DieselDoghouse]

In the less than obvious category if there's an electrical fault the ABS can light too - I had done work on an accessory that shares the ground stud with the ABS controller unit, grounded to the left fender. Must not have snugged the bolt - ABS lit from the time I restarted the truck until I retightened the bolt!!

 

[Cooker]

DarrellB,

Do you have the part number and price of the part. One dealer here wants $73. 50 just for the part.



Thanks,

Ryan

 

[wtrenholm]

On the ABS and red brake lights coming on. First; do you have Rear Antilock or Four Wheel Antilock? There are numerous conditions that will disable either system and turn on the warning lights.



Some basics:



RWAL- rear antilock- has one speed sensor in the rear diff on top. It has enough hardware to modulate pressure in both rear brakes at the same time.



4 Wheel ABS- has three speed sensors, one in the diff (same as RWAL) and one in each front wheel. It has more hardware to control the rear wheels together and each front wheel can be modulated indivually. If you have 4 wheel ABS you will have a Hydraulic Control Unit and Controller on the left front wheelhouse.



Remember if your truck is 98 or newer, it uses the ABS rear (even with 4 wheel, I think) wheel speed sensor to calculate the actual speedometer reading. It works like this: the speed sensor tells the ABS controller the axle/wheel is turning with a AC sine wave. The ABS controller calculates pulses per mile with the tire size that is programmed into it using the DRB, then sends the signal to the PCM (engine controller) via a dedicated wire. The PCM sends the signal over the BUS (info network that connects to various controllers) to the instrument cluster. Which then interprets the signal and makes the speedo read. So 98 and newer means: No Speed Sensor signal = No Speedo or cruise.



Things to check:



Check all fuses for power. In the older Rams blown taillight, back up light or back-uplight fuses can cause ABS or Air Bag lights to come on from lack of various power feeds to the module.



The rear speed sensor and jumper harness is prone to corroding inside the connectors. Unplug and look for green crap growing on the pins. I've had em where there are no pins left. Also inspect the harness for any road debris damage. Mine melted on the exhaust on my '94 gasser. Sensor resistance spec is 1600 - 2300 ohms.



Lots of stuff causes the ABS to come on. An hour of shop time is cheaper then a wrong part. Please don't just throw parts because that's what fixed someone else's truck, maybe it will-maybe it won't. Yes, there are pattern failure that are common, but I fix lots of problems with wiring and ground repairs.



Sorry to ramble on, HTH.



Wayne

 

[KennyM]

Wayne, Thanks for the info. One question, My speedo worked, and cruise worked, but the dealer said the sensor was bad. (shorted) That means straight DC, no sign wave, right. I did notice that the speedo was off about 5MPH when compared to the Tach. After the fix All was normal again. I was thinking the sensor was just acting as a correction factor. And it's main duty was for the ABS. Please tell me if I'm way off. Ken

 

[wtrenholm]

Ken,



One of the controllers may be able to use some kind of back up data to ball park vehicle speed. They do all kinds of back up stuff that is secret. My Kelsey Hayes stuff states the rear sensor is used to generate the original signal. GM trucks (sorry) use ABS sensors to generate vehicle speed the same way, being they run Kelsey Hayes ABS.



Your right that the sensor makes it's own signal, so if it's shorted it would be dead and no AC signal to the controller.



Now I'm all confused on what they're doing. I guess I'll have to unplug mine and cruise around with the DRB on it to see what kind of info is available. Time to spend some more quality time with my truck.



Working on this stuff can be real puzzling sometimes, the manufacturer never gives you all the info on the whole picture. Just enough info to "fix" it. I want to know what's going on and why. I think they want to kick our butt and make it more difficult.



Wayne

 

[Slick]

ABS Light

Had the same problem with my 98 Dakota. It was the speed sensor!!!

 

[DarrellB]

I'm at work now but when I get home I'll look on the invoice.



Big D