Its been a couple of weeks since I last reset computer from previous PO420. Light came back on again. I'm assuming its the going to be the same code - did some researching in the archives concerning the PO420 code and realize it's the O2 sensor or cat. Bought the O2 sensor for the front manifold and wondering if the rear manifold sensor is the same? I bought the sensor thinking I had to replace the sensor on the f. manifold, but after reading the archives, saw that many people replaced the one on the rear. Called Ford and store where I purchased sensor from and neither have been much help. Ford lists only two sensors and Advance Auto lists three, and none of which have the listing of O2 sensor for r. manifold.
You can be Phil too if you'd like. 
