service and abs light always on

in august i bought a 2dr automatic sunfire year 2000 and i keep having the same problem . the ABS light and service light always go on yet the ABS works fine. everytime we bring it to teh garage they say they fix it but the next day it goes on again. can someoen help me with this please. what should i do, is it just a problem with the electrical system in teh dash and how do i fix it???

I own a 2000 sunfire standard, and you are not alone, my engline light is always turning back on no matter how many times i get it checked. they problem it says is the O2 sensor is tripping it off but i have not had any difficulties, i think it is the computer, sunfires and some other pontiac cars have been known to have computer problems, and my friend had the same problem with his car as mine and replaced the sensor and a few otehr parts numorous times. so im not sure what to do but if u do find out please let me know.
thanks
kyle

ya i checked for the O2 sensor but it is not that