So I keep getting the CEL P0420 on my 2004 WRX. The first cat after my turbo has gone bad and it is at least $1000 to fix it with the stock cat. I currently have a 3" SPT cat back exhaust on the car along with a SPT intake. Due to the price, I would like to go full stage 2 and buy the Cobb catted down pipe along with the V3 AP. Has anyone else done this modification? I live in an area where my car does get sniffed for inspection, so everything needs to pass. With this modification, will it ruin my O2 sensor/sensors and will I always have a CEL on in the car? I really appreciate any comments/suggestions.