Technical Braintrust --> Anti Lock Dash Light ON! (13 years long issue)

[ADA///M]

My light doesnt come on until I start rolling....if it doesnt come on at all, the ABS acts crazy and the car will barely stop.

I'm hoping its just needing new sensors all around.

[hardtailer]

Unplug all 4 wheel speed sensors and make a mental note of how the ABS light behaves upon ignition on, start engine, running engine and pulling away up to a speed of at least 10 mph.

Reconnect a single speed sensor. If the abs warning lights behaves exactly as you memorized, the sensor , connection and/or loom to the ABS ecu is defective.
If the light comes on when pulling away, then that sensor is fine.

Repeat with all 3 remaining wheel speed sensors but remember to check a SINGLE sensor at a time.

[hardtailer]

Got this little gem off the SIG mailing list, originally posted by Don Fields

[CamayroZ]

Unplug all 4 wheel speed sensors and make a mental note of how the ABS light behaves upon ignition on, start engine, running engine and pulling away up to a speed of at least 10 mph.

Reconnect a single speed sensor. If the abs warning lights behaves exactly as you memorized, the sensor , connection and/or loom to the ABS ecu is defective.
If the light comes on when pulling away, then that sensor is fine.

Repeat with all 3 remaining wheel speed sensors but remember to check a SINGLE sensor at a time.

This is very good advice. And it is very easy to also measure each sensors resistance.

[ADA///M]

Unplug all 4 wheel speed sensors and make a mental note of how the ABS light behaves upon ignition on, start engine, running engine and pulling away up to a speed of at least 10 mph.

Reconnect a single speed sensor. If the abs warning lights behaves exactly as you memorized, the sensor , connection and/or loom to the ABS ecu is defective.
If the light comes on when pulling away, then that sensor is fine.

Repeat with all 3 remaining wheel speed sensors but remember to check a SINGLE sensor at a time.

Thank you!

[ADA///M]

This is very good advice. And it is very easy to also measure each sensors resistance.

Do you have to measure it while the car is rolling?

[hardtailer]

Measuring resistance of a sensor can be done stationary. Search for the spec but generally speaking either 0 or very high (off the scale or out of range) resistance means bad sensor or bad (wiring) pig tail.

Should you want to measure the signal by means of an oscilloscope or a Volt meter (set to AC!) you want the wheels turning.

[ADA///M]

Measuring resistance of a sensor can be done stationary. Search for the spec but generally speaking either 0 or very high (off the scale or out of range) resistance means bad sensor or bad (wiring) pig tail.

Should you want to measure the signal by means of an oscilloscope or a Volt meter (set to AC!) you want the wheels turning.

When i was half-ass checking them recently, I noticed almost all of my connectors on the harness side were falling apart, so i can't tell which way they should plug in. Does it matter (i.e. polarity)?

[CamayroZ]

During my CSI work, I did not make any measurements myself, since I was able to troubleshoot my issue to the incorrect ABS tone wheel (ring).

However, I did remove all my wheels, checked the sensors, checked the wiring, connectors, etc.

**One of the experts should verify this: ** When I looked at the ABS speed sensors at close up, they looked like the old style "Magnetic pick up" sensors and not the newer "hall effect" type sensor. Therefore, they should just be a "coil" or "inductor" that is activated by the passing of the ferrous ABS tone wheel. Basically, a sine wave is generated as the ABS teeth goed by, and thus why you would need an oscilloscope to look at the actual signal which is only generated when that ABS wheel is spinning! :(

Therefore, the resistance of the sensor will be low, since they are basically a "coil" or an "inductor", and polarity should NOT matter.

Good luck to you!

[jimmy p.]

During my CSI work, I did not make any measurements myself, since I was able to troubleshoot my issue to the incorrect ABS tone wheel (ring).

However, I did remove all my wheels, checked the sensors, checked the wiring, connectors, etc.

**One of the experts should verify this: ** When I looked at the ABS speed sensors at close up, they looked like the old style "Magnetic pick up" sensors and not the newer "hall effect" type sensor. Therefore, they should just be a "coil" or "inductor" that is activated by the passing of the ferrous ABS tone wheel. Basically, a sine wave is generated as the ABS teeth goed by, and thus why you would need an oscilloscope to look at the actual signal which is only generated when that ABS wheel is spinning! :(

Therefore, the resistance of the sensor will be low, since they are basically a "coil" or an "inductor", and polarity should NOT matter.

Good luck to you!

Correct, the old style are simply inductive. They are nothing like the newer modern sensors. The E30 ABS computer is simply looking for matching voltages.

[nrubenstein]

Its been a while since I had the two versions side by side but the hub assembly itself "should" be identical, just the ABS ring should be different. I dont remember any noticeable to the eye differences other than the ABS rings. At least for over 20 years I have thought they were identical parts other than the ABS ring.

I have a piece of PVC pipe I use to install the cup, its the diameter of the recess, then I just tap it on.
No grease on the bearings, they are sealed.

I've compared Genuine BMW E30 M3 hubs to the E28 hubs. The "Genuine" hubs from both SKF and FAG carry E28 part numbers. The only difference was the somewhat halfassedly pressed on ABS ring.

I will note that the Genuine SKF hub didn't fit correctly. I ended up swapping it out for an E28 FAG unit.

[CamayroZ]

Since we can post pictures again
I am bumping this thread with pictures and part numbers for future folks chasing down ABS light issues. Mine was due to incorrect E28 hubs. Thanks again!!

[nrubenstein]

Hopefully your SKF hubs don't have oversized hub centers like mine did.

[Ron ///Man]

I can't tell you how many E30 M3's I've seen with incorrect front hubs. People either just don't pay attention or don't care and just slam the 5 series bearing hubs on while ignoring the small details about swapping the ABS rings and picking the "correct" 5 series hub that has the right hub centers...

[nrubenstein]

I can't tell you how many E30 M3's I've seen with incorrect front hubs. People either just don't pay attention or don't care and just slam the 5 series bearing hubs on while ignoring the small details about swapping the ABS rings and picking the "correct" 5 series hub that has the right hub centers...

This was a Genuine BMW E30 M3 SKF picked up by me from the parts counter that had the wrong hub center. Just slightly oversized, so you could make it work, but it was ugly. After fighting with it for a while, I replaced with an E28 FAG unit (ABS ring swapped).