ABS Problems...need help
 

I have ABS and brake lights on in my truck. The lights come on after 5-10 minutes of driving and stay on. While they are lit the brakes work great....before it lights the ABS cycles at slow speeds making braking unpredictable and sporatic.

I had codes checked and is showed loss of contact with rear sensor, so I replaced it. It did no good at all. It still acts the same.

I checked for bad wiring and did not see anything under the bed.

When looking around the ABS control area I found to interesting things. One, there is a wiring harness with two ends bundled up like it was that way from the factory. I thought the two ends would go together, but they would not. I suspect this has nothing to do with ABS, but thought I would mention it. Also, there was a ground wire loose under the ABS controller that was taped to the harnes and really appears to have been that way from the factory. On my 01 I would have swarn this was connected somewhere around the brake controller.

Can anyone help with this?

Thanks!

Update.

I hooked up the loose ground and nothing changed. I topped off with fluid(was 1/4" low) and it did not help.

Right now the ABS pump is running all the time from what I can tell untill the light trips....brakes are there, but are hard and sluggish. Then at about 5mph it stops running and they grab. PITA!!!

I have the same problem and nobody seems to have any answers. good luck

You need to check the two wires from the sensor to the abs computer. You most likely have a broken wire. The code is telling you that the rear wheel circuit is at fault. Pretty simple to test.

On mine the code for the rear sensor was an old code and not a current code. I talked to a mechanic at one of the dodge houses that was recommended for actually knowing how to trouble shoot and he said it was the abs module itself. I also talked to a guy who used to maintain a fleet of dodge trucks and he said the same thing. So, I have ordered another one and will report back when I get it in. I actually just bought this truck, was suppose to be in perfect mechanical condition, and the jack wagon I got it from was suppose to "make it right", but he has yet to send any money...figures. Ain't nobody honest these days.

Thats BS as far as I am concerened. That code is relevant. You need to get a scan tool on it that will monitor wheel speed. If you did not do this you might as well believe in the tooth fairy. You most likely will see no data from the rear sensor. You can easily unplug the sensor at your abs module, Jump the two wires togeather at the rear sensor and ohm it at the module connector. I will just about bet you will have an open circuit which will lead to a broken wire right at the main harness at the fuel tank. You asked for help and now you got it. If you dont take the time to ohm the wires as I have told you.........Well I wont waste my time answering any more of you questions.

Your pretty right on here, but if it were me I would unplug it like you said at the module, leave the sensor wires connected on all 4 wheel ends, then ohms check all 4 sensors there at the module harness plug. You should get pretty much the same reading at all 4 wheels.
I can't tell you what the specfication is for the sensors though. At work on big International trucks with "Bendix ABS" systems, the sensors are around
2.1k ohm.

While I will agree with you if we knew the values that would be a good diagnose. The codes he claims are/were rear sensor related. History codes may of shown other issues. This is the problem when the issues is not properly diagnosed. The poster has already replaced the sensor which most people do and it fixes 75 percent of the problems. The othe 25 percent have issues. If you dont have the scan ability to monitor in real time the wheel speeds then you are tossing parts at it. I made it simple. Unplug the module, rear sensor. Jump the wires either end and ohm them. Open fix the wires. We fix many with wires broken as I said right behind the tank.

As I stated in my first post, I already checked the wiring....but, I did not ohm it.

Do you know of a good place to find a wiring diagram for the ABS system or better yet which plug and pins the rear sensor are? I can ohm the wires easy enough but I have already inspected them and found no external breaks. It would have to be something inside the insulation....which I dont see causing a constant open circuit, but it might show up on an ohm meter if wiggled while testing.

Do you happen to know if it is a magnetic or variable reluctor type sensor? I dont have a scan tool, but I can oscope it while driving and should be able to tell if it is working.

The module is already on the way and I found a used one for $20 so I will have it one way or the other. If nothing else I can sell it and make some money since it retails for $523 :).

You are absolutely right about finding an open. And you don't really need to know the values to see if all the sensors have "relatively" the same ohms readings. An open is an open, no matter if the sensor is plugged in or not.

You eliminate one step, by not unplugging the sensor and also get to check all the sensors. Then, if you have an open or a very different reading between sensors then you start unplugging and jumping.

Just my .02. Either way will tell you how the wiring checks out in the end. So, we will see what his next step is.

Well, I was under the truck working on a diff pan leak and decided to check out the wiring at the fuel tank. I found that the wire is in a plastic protective sleeve that was broken and rubbing the wire. There was a hole in the insulation so on the off chance that the wire had also broken from working back and forth, I cut it, soldered it back together and wrapped everything back up.

It did not fix a thing.

So, since I can't find a wiring diagram(other than to buy one for $30) I will try the module when it comes in and go from there.

PM me and I can give you schematics...and all abs trouble shooting/diagnosing information for a 3rd gen..i have used it as a quideline for earlier trucks..

Sent a PM, but did not get anything back. I just put the new(used) module on and the problem is still there to some degree. The pump is not kicking on and running solid, but there is some ABS "activity" on a rolling stop at low speed. A wiring diagram would be great if anyone has access. I have not been able to find one.

Also, what kind of scanner does it take to check wheel speed and does anyone know for sure this can be done on the 99. No one around here I talk to seems to know about that....

You can check wheel speed sensors with a DSO, ie; Snap-On Vantage. It will not give you wheel speed, it will show the square wave pattern of the sensor. If you have the pin-out for the ABS plug you can set the Vantage up to check two speed sensors at once and compare the values.

Rick

Thanks, Rick. I will have to see if I can find one of those and borrow it. I know a couple of mechanics.

If I can find the pin out I can think I can use my oscope function on my meter to check the individual spensors at speed and compare the frequencies, but that is proving hard to find. I guess I can get a friend to ground pins one at a time and sort it out....gonna have to figure something out cause I dont like things not working right.