Originally Posted by wrx_snobordr
THEY not I, when doing my 30k overhaul just placed my stock airbox back on and ditn bother to slide to two tabs in the back under.
Nope - this should be it. End of story
Smack the "service manager" upside the head next time you see him/her! And I agree with PAWRX - never heard of a catback causing a CEL, nor can I imagine it causing a front o2 sensor to go bad- the only thing I can think of is if you shoved banana's or melon's in there to block it off, but that's just retarded. Otherwise, you can run without a catback if you want to... of course, the floor might get a little warm... and the car might be a little loud...
but doing any of that shouldn't cause your front o2 sensor to do anything differently.
Sounds like you're right on the money with disconnecting the battery for a little bit. That should clear your code, and you'll know within a few driving cycles whether or not you "fixed" (their) your problem!