ABS/Brake light ON

[jbone]

Just a sanity check guys, looked at pads about 4k ago, around 36K--now has 40k... ... I'm thinking new pads will fix this problem, but as we all know can't check old threads so wanted to rehash this before I spend Saturday fixing something that won't turn those lights out..... Guess I'm asking if "you'll" (check location) agree??? R, J. B.

 

[DennyDay]

ABS/Brake light

Didn't post year, but if it is 98. 5 or newer, does speedo bounce around? Look at the speed sensor, yank and clean, and re install

Good luck!



Denny

 

[rcaldwel]

ABS/Brake Light

I just encountered this on a trip to Calif. I was pulling a small trailer. It turned out to be the Rear Wheel Speed Sensor(RWSS) that sits on top of the differential and sends info to the speedometer etc. It is a magnetic pickup and does get dirty. I first tried pulling it and cleaning it off as suggested by other TDR members. the ABS/Brake light still was on. I got a new RWSS from the dealer ($31. 49) replaced it and the lights went out.



One clue was that the speedometer would not show any speed until around 20 - 30 miles per hour then the needle would jump to the correct speed. this would happen every so often and was the real clue to pointing out the RWSS.



Hope this helps.



Bob Caldwell

 

[rrausch]

I've got a '95 2500 2WD and the ABS light came on after I replaced the front pads, and put speed-bleeders in and bled the brake system.

I thought WTS! So my cure was drive about 35 and hit the brakes and lock the rear up. It worked, light went right out. Clumsy but it worked.

 

[thejeepdude]

WOOHOO!

I knew I loved you guys! I love my CTD, and was just raving to my GF about how I don't need the 2003, because I like my '99 better anyways, and I can just spend the extra $$ on modifying it, blah blah blah... then all of a sudden my brake and ABS lights come on. I thought for sure "it's electrical, dealer's gonna screw me out of $99 to put a computer on it for 2 seconds and tell me a $20 part is bad". So now I get home... search the TDR... viola! EXACTLY my symptoms, am about to go try the RWSS right now. I already tried locking of the brakes at 50... didn't do much more than leave a solid stripe of my new BFG A/T's on the road. :\ Anyways, just wanted to say thanks to everyone who makes this community rock! I'll let y'all know how it goes...

 

[wtrenholm]

jbone,



Brake pad replacement will not turn the lights out. The controller has no way of determining this. I don't recommend just slamming in a rear wheel speed sensor, while it is a common failure almost half of the trucks I fix are not this sensor. Last thursday it was a LF sensor, the one before that was a blown fuse. Depending on year and system you may be able to access trouble codes yourself. Post more info and I'll try help more.



Wayne

 

[thejeepdude]

YAAAHOO!!

It's a great day! Well, thanks all. It's only been 2 days since the BRAKE/ABS lights came on and I had the speedo symptoms (speedo didn't react until 25mph or so). Saturday I took the RWSS and cleaned it, but that didn't do anything. There were only a few small filings of metal on there anyways, so I figured it was just shot. Well, this morning (Monday) I stopped by the dealership on the way to work and picked one up. After seeing so many people with the same issue, I was pretty sure the RWSS was the problem. Well, 5 minutes ago I swapped 'em out, and sho' nuff, that fixed it. It took me less than 5 minutes to replace. One 1/2" wrench on the top nut that holds it and the brake lines down, and one small flathead to pry the thing out. Anyways, just wanted to report the good news, and while the last post here indicates that there are other causes for this problem, if you're having these symptoms, I wouldn't hesitate to pop the $40 for the RWSS and see if it works. That's still cheaper than paying the dealer a 1 hour minumum to diagnose it. Again, thanks to everyone that makes the TDR rule!! My baby is well again.

 

[thejeepdude]

half?

Originally posted by wtrenholm

jbone,



Brake pad replacement will not turn the lights out. The controller has no way of determining this. I don't recommend just slamming in a rear wheel speed sensor, while it is a common failure almost half of the trucks I fix are not this sensor. Last thursday it was a LF sensor, the one before that was a blown fuse. Depending on year and system you may be able to access trouble codes yourself. Post more info and I'll try help more.



Wayne

Wayne, I respect your troubleshooting skills, and the point you make here. However, by saying "almost half the trucks I fix are not this sensor", one can deduce that "just over half the trucks you fix ARE this sensor". I still think that for $40 and 10 minutes, and a 50/50 or better chance that this will fix the problem, it's worth it.



I have a question, though... on the trucks you fix that didn't have a RWSS problem, were the symptoms exactly the same? The symptoms that I had were ONLY these three things... otherwise everything functioned completely normal:



1. Brake light on

2. ABS light on

3. Speedo would not register speed until I reached 20-25 mph.



Have you seen these exact 3 symptoms and only these symptoms while the RWSS was not faulty? If so, how can one go about testing whether it's their RWSS or the LF sensor or something else? I don't count the blown fuse incident, as that should obviously be the first thing you should check as soon as any electrical related problem shows up, but I'd like to more fully document this problem in the event there are other causes, given its high incidence and the chance someone else could be searching this thread later for the same issue.



Thanks,

Josh

 

[wtrenholm]

Josh,



I haven't replaced a RWSS on a 98 or newer, so I haven't come across the three symptoms you mentioned. On pre 98 they still use the Output Speed Sensor on the trans or t-case for vehicle speed. It seems 98> w/4WAL use the RWSS for primary vehicle speed, then use data from the front sensors once a codes sets for the rear sensor. Which would explain the no speedo until 20 mph. I need to spend some time causing failures on my truck to see how it reacts to various problems.



There are lots of changes in the RWAL or 4WAL systems over the years. I know some but not all. My info is based of what I learned when I worked at the dealer, what we fix at a vo-tech where I teach and playing with vehicles for class. I did a lot of messing around with the RWAL system on my 94 gasser. Playing with the 4WAL system on a 95 gasser (the LF sensor truck) I found major differences on how they monitored the sensors and code setting paramiters.



I just don't like throwing parts at vehicles, but I understand that diagnostic time is more money then a $40 guess sometimes, especially if it's the correct part. Accessing trouble codes on some earlier systems or doing some simple volt/ohm checks cost nothing so why not check these first so you are sure of your repair before spending a dime?



My thoughts,

Wayne