After a couple hours of wringing off bolts and cutting one off (ones on cat were very corroded) I installed my new Greddy Evo. Started the car to listen to it, turned it off. When I went t drve it later, the check engine light came on and hs stayed on. I reset the ECU and that did'nt help. I have a 2k cali spec so no O2 sensors were disturbed. Can anyone explain this? And yes I tried the search first and at least found out there is a good thing about the cali spec, no welding in an o2 bung!

 

I'm surprised to hear that. I've had the Greddy Evo on my 2K1 Cali Spec for over a year now and i've never had the SES light go on. I have the Cattman y-pipe and Stillen Hi-Flow too and no SES light so far.

 

Unfortunately there is no way to say whats wrong without getting that code pulled. Go to autozone and get it pulled and come back. I dont see any reason a check engine light should come on with a catback. No reason whatsoever, might be coincidence.

Dixit