I just got my first CEL. I put an aps 3 inch exhaust on with the high-flow cat. Have about 500 miles on it, and now a cel. It happened after I got on it hard. I checked under the hood and the turbo seems to be hotter. My guess would be the o2 sensor. I've unplugged my battery to clear it for now but if it comes back tomorrow i'll pull the code. I've noticed my boost jumping up and down and up again. I was told that I have boost creep, but I shouldn't worry as long as I didn't over boost. This and perrin crank pulley are my only engine mods. It's an 04 wrx 2.0L. Any thoughts or comments?

 

It will keep coming back. You need to get one of the many CEL fixes that are out there. You can get the wire-in type, mechanical type, or have it fixed via reflash of your stock ECU.

 

Ge the mechanical after I reset my ecu it worked great