[tccrab]

You will need a GM Tech1A scan tool to diagnose and after fixing the problem, to reset the code.
If the problem turns out to be a faulty relay in the ABS system, I've dealt with this in the past.
The relay is made of pure unobtanium new, you will either have to source a used one off another 1990, or perform a mod like i describe in a post long ago.
Do a search for pasts posts by me on ABS relay mod.

Crabs