my ck enging lite is on .i have put a new catv on and a new flex pipe.also a new

Have it scanned at a shop not a parts store .The code(s) will tell you what system(s) are affected and help lead you to the proper fix. If the exhaust repair (catv?/flex pipe) is near an oxygen sensor , check for leaks , even a small one can affect it's readings causing the MIL to illuminate.(MIL= malfunction indicator lamp)Good luck.

What code are you getting? Important.