Finding bad ABS sensor

Eyvind Spangen eyvind.spangen at
Thu Nov 8 18:11:54 EST 2001

I'm having a problem with one wheel speed sensor on my '90 200TQ. The
ABS will switch off in about 30 seconds from start if I'm driving, but
will stay on for ever if I just leave the car idling. If I try an ABS
assisted stop, the right front wheel will block, the left front wheel
is almost not braked at all. Braking distance is several times longer
than without ABS. In addition, I can hear the ABS hydraulic unit run
when I drive slowly. It will just run something (the brake pedal gets
hard too) for the 30 seconds, then the whole system shuts down. I've
tried measuring resistance on all sensors/wires, everything OK. I've
tried repositioning the front sensor with new caps, still no effect.
I'm thinking bad sensor, as the front wheel bearings were replaced by
the previous owner, which probably didn't reposition the sensors
properly. The ABS was just disconnected the whole time he owned the
car because of this problem.

I've borrowed an old multimeter, but the lowest DC voltage setting I
can measure is 10 volts, with the sensor output being 0.5 volts, I
guess this won't work. I don't easily have access to an oscilloscope..


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