Posting in both Tech and Diesel since is shared system for 1991.

Started working on ASD system and may have ended up with two malfunctions - the ASD Activtation (sensing slip) dash bulb was apparently out AND the right front ABS sensor was identified by setting a code in the ASD module.

The ASD module pin is reading 8.15 VDC for the right front sensor and 4 VDC for the left front sensor - both are supposed to be 4 VDC when the wheel is spun by hand at about 1 rev per second. In spite of this, I don't get an ABS malfunction light.

My understanding is the ABS module changes the millivolt AC signal coming from the ABS sensor to the DC signal the ASD module sees - anyone know if this is accurate?

If true, the AC signal coming from the wheel sensor could be in spec and the ABS ECU could be developing an out of spec AC signal that it is sending to the ASD module. The other alternative is that the ABS sensor is actually developing a bad signal, but it doesnt matter to the ABS ECU because it reads frequency not voltage?

I have reviewed 42-720 "Electrical Testing" test program procedures, but the alternatives don't show a mechanism for ABS ECU pin to ABS speed sensor pin testing with an ohm meter ... any advice on how to do this? I hate idea of just replacing a sensor when it's unnecessary ...and expensive.

Another alternative is to find a reasonably priced used sensor ...havent been able to locate one, yet ...

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg