I have a cold air intake 3.4 pulley 3'' downpipe high flow cat and U-bend delete on my 2002 grand prix GTP why would the service engine light be on?

It may be an oxygen sensor issue. I had a 2002 Mustang GT with similar set up and had the same problem. The manufacturer of your high flow exhaust system should make a new sensor that takes the place of the stock one that sends a false signal to the emissions control and gets rid of the "check engine" light. There can be several reasons for the light to come on. It can be because the O2 sensor has been eliminated with the U-bend delete or it can sometimes be related to the CAI modification. Get your engine scanned to know for sure. For related info on your modified engine see the postings on www.clubgp.com Hope this helps. "G"