Help! Anti-Lock Light is on

[Toms73NovaSS]

a analog multi meter would work better than a digital because you will be able to see the needle jump up to max and down. With digital it will just be a random number and not have a chance to actually see a value.

The proper thing to use is an oscilloscope with a recording feature so that you and take a look at a full rotation of the wheel and see if there is and inconsistency in the signal thru a full rotation.

[Toms73NovaSS]

Does anyone know of a write-up on testing the wheel sensors? I have a multi-meter.

You should be able to put each lead to each plug end and set the ac setting to the smallest setting. The amount of signal will be small due to the small coil in the abs sensor.

[bimmerboy12]

You should be able to put each lead to each plug end and set the ac setting to the smallest setting. The amount of signal will be small due to the small coil in the abs sensor.

My multi-meter is digital but I can borrow an analog. Would you disconnect the sensor, put the leads in the sensor plug, and spin the wheel slowly to watch the needle bounce? I guess that wouldn't work unless you put it on a resistance setting?

[bimmerboy12]

bump for help, my anti-lock light is popping on right after I start moving now.

[Hallen]

AFAIK, there are two sensor type inputs to the system. The wheel speed taken through the ABS sensors in the wheels and the vehicle speed taken from the speed sensor in the diff (most likely). If the vehicle speed is below a certain value, the ABS should be deactivated. You don't want the ABS working when you are stopped for example.
It could be that your speed sensor is going out. Does your speedometer jump around at all?
The only thing you can do is test stuff as described here, then start replacing parts starting with the most likely and the least expensive. Try one new wheel sensor and move it around to the different wheels and see if that helps. Try a new speed sensor on the diff.
If you are sure the brake system has been bled properly, then the next step sounds like a new ABS unit.
You can drive the car without ABS. Just pop the ABS relay out and drive it that way. You just have to be careful to not lock up, but you won't be having the ABS kick in at low speeds which could potentially be more dangerous than a lockup.

[dark89e30]

Did you clean the toothed rings yet? Very important. Look carefully for sensor wire damage also before you start throwing parts at it. And just in case, you could make sure the rings are actually the same, as well as correct.

[bimmerboy12]

Thanks for the help guys. I did clean out all the teeth, and i know everything is correct because the ABS has worked fine for the last 7 years. I don't think it is the speed sensor in the diff, because this problem started when i had my open 3.73 and didn't change when I installed the 4.10 LSD. I may just get a couple used sensors and start swapping to see if I get improvement. I just hope its not the ABS computer or pump.
Could this problem be caused by air in the lines?

[Hallen]

I doubt air in the lines is the problem. If you have bled the brakes anytime lately and got all the air out you are good. Sometimes, I have heard that air does get trapped in the ABS system and a good way to get it out is to activate the ABS system to move fluid through then rebleed the brakes. Sounds like you have been getting the ABS to actuate too much.
That is why I am thinking it is the speed sensor. Are you sure there are no shorts in that wiring? Tough to check all of it I know. I hope it is not the ABS unit too. That is an expensive item.

[DCColegrove]

You have a bad sensor, the diff pulse gen. doesn't have anything directly to do with the ABS. test the continuity of all the sensors (I don't have the spec handy here at home but I'll bet one is way different from the rest.

Look at then too physical damage will cause problems even if the coils are intact.

[bimmerboy12]

Just to wrap this thread up- it ended up being a speed sensor. I bought 4 used ones, and just started replacing them until it was fixed. I tried continuity testing them and that did not work as they all registered similar values. Thanks for all your help!
Brian

[txleadfoot]

Thanks for the udpate, I have the same issue. Do you have any good spares?

[StereoInstaller1]

Thanks for posting in this thread, guys. especially Mr. Colegrove.

The wifes car has the same issue, but just a light, no oddities in the brakes.

I will get on them there sensors shortly.

Thanks!
Luke

[lordofthewaters]

If it's just the light, have you checked the relay?

[el bob]

My light is on all the time now too. I guess I'll check the sensors. I hope the continuity test makes it obvious, because getting spares will be a bitch.