Today my ABS and ASR inop lights came on. They did it once before but shut off the next time i started the car. This is on a 1996 Z-28. My question is since its both lights that are on that would mostly likely point to a sensor in the rear of the car, right? If i go up to autozone and get the free otbII scan will that show me which one or do i have to do something else. Any help would be gratly appreciated because my dash looks like a chrismas tree right now.

they should be able to help look up the code, but you cant always just buy the part that the trouble code is for
you should diagnose it to ensure that the part has actually failed and that its not just a wiring problem or something else

but getting the code is the best way to start

ur relay is gone look at ur fuses and relays under the hood it should be the one labled abs

I have the exact same problem as well, and I hear a like chattering noise under the dash in the passenger side footwell, it sounds like a relay, could this also cause the problem.