ABS vooodooooo can be annoying when it rears it's head.
My system on my '95 was working perfectly well(or so I thought) for over a year, until....
Replaced the battery. Yep that's all I did was remove/install a battery. Then I had a front abs sensor fault, wouldn't clear.
I thought WTF could I mess up changing a battery.....that would affect an ABS sensor.
Long story shorter, I checked the sensor gaps and ended up adjusting the gap to correct the fault.
So, just sayin, anything is possible. You may want to double check the cleanliness of the multi-pin plug contacts at the controller, and make sure it is seated well. That one can be a real bugger to connect completely.