Stupid Engine Light

O.K. SO I'M SURE YOU ALL ARE TIRED OF THE SAME QUESTION, BUT ANY HELP YOU CAN GIVE ME WOULD BE GREATLY APPRECIATED.
JUST RECENTLY I PUT A H PIPE AND BBK MIL ELIMINATORS ON MY 98 GT AND RESET THE ENGINE CODES BY UNPLUGGING THE BATTERY. THEN ABOUT HALF A DAY LATER THE DAMN LIGHT CAME ON AGAIN. I SENT THE MILS BACK AND GOT A NEW PAIR THINKING THEY WERE FAULTY. THEN GUESS WHAT?? SURPRISE, SURPRISE THE LIGHT CAME ON AGAIN. I NEVER HAD A PROBLEM WITH THE LIGHT BEFORE THIS. IS THIS A BAD BRAND OF MILS (BBK)? WILL ONE OF THOSE SMALL STORE BOUGHT COMPUTER TROUBLE CODE SCANNERS TELL ME WHICH 02 SENSOR IS TRIGGERING THE LIGHT?