I just installed my downpipe last week and I just threw a CEL today. I used the mechanical fix with the o2 sensor. I have a 04 wrx. Has anyone else had this problem, and how did you fix it. I'm thinking that i'm going to have to buy the resistor or whatever. I'm thinking about buying the fix from Gruppe-S, is their fix proven to work?

 

Have you had it scanned to be sure it's the P0420 code and not something else?

 

yeah I'm going to do that once when I get a chance, but i'm pretty positive that it is the o2 sensor code, but I'll make sure.

 

Did you reset the ECU after you installed the downpipe and the mechanical CEL fix??

When I installed my downpipe on my 04 I used the mechanical CEL fix and got a CEL after about 30 miles, I reset the ECU and have not seen a CEL since (about 350 miles).

 

I had the battery disconnected during the install. The cel just went off by itself when i got home from a long trip, and it hasn't come back, i dunno. I'm just happy it's gone.