Lots of info on this. Use the forum search tool and search for "P0420".
Doubt it's the gas. Is the light still on? You could put some 93 octane gas back in the tank ASAP and let it mix.
If the light doesn't/hasn't gone out, you probably have a bad O2 sensor or possibly a bad or partially plugged CAT. Read the other threads for more info.
04 6MT, Navi, WDP, chrome wheels, ASPEC suspension (08W60-SEP-201B), Clifford Matrix 50.7X RS/Alarm, Huper Optik ceramic tints. Original owner....
Last edited by nfnsquared; 10-04-2010 at 06:32 PM.