Hi,
I personally had the P0420 code appear in my '97 Contour SE V6 3 years ago.
(On the advice here and elsewhere) - after I cleared the code (via scanner) -- I put a can of Berryman's B12 into EVERY gastank fillup for about 5 consecutive fill-ups.
The CEL never re-appeared.
Now I put a can of B12 *or* Seafoam into the gastank every second fillup.
Gerry
BTW, if you need 'instant gratification' -- then instead of 'diluting' the B12 with a full 15 gals or so of gas -- then 'introduce' the B12/Seafoam into the UIM via a length of rubber vac. tubing. Be warned tho', Seafoam tends to smoke ...whereas B12 does not.
