The ABS is not diagnostic capable.

This thread where I worked on the same system on my Audi might be helpful: http://www.peachparts.com/shopforum/tech-help/288450-trying-troubleshooot-bosch-abs2.html

As others noted the ABS computer lives in the engine bay by the battery, but you could put the car up on jackstands and spin the wheels. I think you could use a simple multimeter and look at the AC voltage coming off of the sensors to get an idea which one might be giving trouble.

-J

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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.