ABS problems on my 93 jimmy

Ok, fellas,

I own a 93 gmc s-15 jimmy, 4.3l vortec. My anti lock brakes are having serious issues. My front left caliper engages and of course it pulls hard to the left, but, sometimes I have a hard time even getting the petal to go down. The right side doesn't seem to be working. I pulled the wheel off and the caliper moves in and out when brake is applied, just not when driving. I've bled all the brakes, their all new front and back. I pulled 2 codes from it and got 12 and 23. Not sure what they mean. Anyway, when it started doing it I found a little ball of metal about the size of a marble pinned in between the sensor and I guess it a gear of some sort on the wheel bearring. Took it out and cleaned everything. Still nothing. Would any of you guys be able to steer me in the right direction. I've ordered a new sensor for the right side but not sure if that will fix the problem. How do I reset the abs system after. I change the sensor. Any help would be appreciated.

My problem ended up being my abs sensor. thanks for your help.