I'm overwhelmed by the gracious responses from the group! Thanks for all the advice so far. I've reset the code (by removing fuses 4 & 11 for 15 minutes), replaced a kind of dirty air filter, put in a few ounces of fuel injector cleaner, and made an appointment next week at the Ford dealership, where the service advisor tells me that for $69 they will find out which of the various and sundry reasons are the true cause of my code P0420 code - stay tuned... (At about 150 miles into the code reset, the CEL remains unlit.) At the present time, if the dealer convinces me to replace the precat, I'll probably go for it, as I am really pressed for time. A major household move is pending to a location where I don't know the mechanics and their reputations. Perhaps I'll initiate another post searching for recommendations of reputable mechanics in the Denver area!!
