Not a 'benz, but it's really similar...

My 88 Audi has Bosch ABS2, just like all of our 80s Mercedes. I'm trying to troubleshoot the system, currently it always thinks a wheel is locking so whenever you apply the brakes the ABS comes on. After driving for a bit the ABS warning lamp will come on and the system turns off. I believe it is a rear wheel because it doesn't affect stopping much. Like a Mercedes both rear wheels are on the same hydraulic circuit, but each wheel has its own wheel speed sensor.

I've checked the resistance of each sensor from the computer's plug, each one is about 1 ohm. I put the car in the air and spun the wheels, each sensor makes some voltage. I checked the wiring diagram and the car does not match. Probably an error in the service manual, but changing the wiring to match the diagram didn't seem to change anything.

My next step will be to have someone else drive while I check the voltages and waveforms with an oscilloscope. The computer lives under the back seat so this shouldn't be too bad.

Any other suggestions? I'm wondering if the control unit could have gone bad somehow?

-Jason

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.