Hey everyone, here is the back story to my problem. First off I have 2005 WRX. Back in the spring I put a Grimmspeed uppipe in to get rid of the cat. I did the resistor mod and it was fine for a few weeks, then I got a check engine light. That same day I received my Accessport in the mail so I installed it so I could check the code. Well installing it must have erased the code because it went away and didn't show up when I tried to read it. A couple weeks later I got my Cobb high flow catted downpipe, installed it and went to stage 2. All summer long I didn't have a problem. Then about a week and a half ago I decided to go back to the stock downpipe setup and uninstalled the Accessport so that I could save some money and sell the downpipe and the Accessport. Well tonight my check engine light came on so I had the code read and it was a P0420. I know that this code has to do with the rear o2 sensor and the cat being below threshold. So what I am wonder is, will having a catless uppipe in cause this code to come up since a cat was removed. If so will a spark plug non-fouler in the rear o2 sensor bung fix this problem or will this cause other problems. Any information will be greatly appreciated.