new to the forum, but have searched it many times. most recent PO420 cel.
2004 wrx no mods, 50K miles
replaced both O2 sensors with oem type bosch. PO420
dealer replaced cat. PO420
mechanical "fix" http://forums.nasioc.com/forums/showthread.php?t=609462. PO420
dealer tells me he can't do anything further till i put the original oem sensors back in (not sure what that means).
i don't hear any exhaust leaks, but doesn't mean i don't have any...
not sure what to try next.