Hi, I have 91 caprice classic. Today I drove home and suddenly ABS control lamp lighted up. I tried brake hard, car went to slip. What is the first thing I have to check? Some sensor? Thank you.

Well first thing you have to do is get it scanned, and see what DTC's are setting. This will lead you in the right direction, whether its a relay, sensor, module, wiring, or pump problem. Without the DTC's you could look all day and not find the problem.

Unfortunately, no diagnostic trouble codes, connected with ABS. 44, 45, 46 and 54.

43 Electronic Spark Control (ESC) Circuit
44 Oxygen Sensor Circuit (Lean Exhaust Indicated)
45 Oxygen Sensor Circuit (Rich Exhaust Indicated)
54 Fuel Pump Circuit (Low Voltage)

I found out brake pads and brake shoes are not i perfect condition, could mailfunctioning ABS indicate this?

there could be brake dust build up on the sensor/teeth on the rotor for the abs

when you do the front pads take the rotor off and look at the teeth on the inside to see if there all still there, and that sensor isnt all dirty.

might help.