After digging through some old posts, I can't find a sure-fire fix for the trouble code P0420 Catalyst System Efficiency Below Threshold (Bank 1). Based upon the mods listed below in my signature, what would you guys recommend?
There are few "sure-fire" fixes for anything... But what usually works for this is an extender to move the downstream O2 sensor out of the exhaust flow a bit. Jan at RMW sells these.