I dont mean to be a pain with all my questions, but im curious.

over christmas I put a cat back exhaust on my car and my CEL came on as I figured it would and it was the 02 sensor. So I got it cleared and a day or so later it came back on, and I repeated the process, and tonight it came back on again so I am wondering if it is really bad and needs replaced or am I going to have to get my ecu chipped to clear it permanatly.

thanks

steve.