Engine light is on. Went to Autozone & was told code P0420 on 2000 Lincoln LS

This is catalyst efficiency low bank 1. This is the ability to store oxygen.Also states running condition. Causes: i have been putting mid grade gas instead of premium would this be the reason. Ps i changed the catalic convertor in 2011 due to the engine light Thanks greg

by in Port Jefferson Station, NY on April 09, 2012
2 answers
ANSWER by on April 10, 2012
If you replaced the Catalytic converter with an aftermarket replacement that may all your going to see in time before that code comes back. The aftermarket converters do not have anywhere near to amount of precious metals that the factory converters have. If it was from dealer you got another problem and need further diagnosis done. Fuel in my opinion should have little bearing.
ANSWER by on April 10, 2012
NORMALLY THE AFTERMARKET CATTS COME WITH A 3 YR WARRANTY SO CK WITH INSTALLER. IF CAR HAS NO OTHER ISSUES CAUSING THIS FAILURE THEY MIGHT BE ABLE TO HELP