I'm sharing my experience in fixing my ABS problem so as to help others that may have the same problem.
The ____!____ light was comming on after the car started moving. So right away that told me that the ABS control unit was ok and that the problem was with the speed sensors. But which one and why?
To easily find which one I did the following:
Disconnect the connector on the ABS control unit located on the passenger side, just to the right of the glove box by removing the two small screws circled in the first image.
Press the small ears circled on image2 to remove the connector. You end up with the connector on image 3.
Using an ohmmeter you should be mesuring ~1000ohm on each speed sensor.
Front Right, PIN 11 and 21
Front Left, PIN 4 and 6
Rear Right, PIN 24 and 26
Rear Left, PIN 8 and 9
In my case, the rear right, (which by the way is to your right sitting in the car), was mesuring 0 ohm, meaning that either the cable was cut somewhere or something was not connected correctly. it was the small connector below the rear brakes that connects the brake pads sensor and the ABS speed sensor, the cable was not pushed in correctly.
This procedure allowed me to find the problem in around 15 minutes, without having to remove every wheels
Stephane, '90 S2
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If the ABS fails after you start moving it has failed it's self test. In my case it is probably the hydraulic ABS pump which attempted to cycle through a self test. It is not necessarily a speed sensor.
I had similar issues: '!' on after driving and all the sensors had similar ohm readings. In my case the car had been in an accident and so I knew which corner to start at so I bought a used sensor fairly cheaply and it fixed the problem.
I do vaguely recall that the failed sensor looked different than the new (used) replacement, the magnet (or whatever that is) that protrudes appeared to be shorter on the bad sensor but it still had the same ohm reading as the others.
Greg East <- Why is my name here?
Loveland, Colorado USA Click Here for my 3-spoke wheel install thread
'87 951 K27/6 7200, Vitesse MAF w/Rogue M-Tune, Tial 38mm, Konis, Weltmeister springs, 968 MO30 sways, vision by IceShark, interior by Classic 9 Leather
BMW CCA Driving Instructor 040212-2901