HAVE CODE PO420 WITH CHECK ENGINE LIGHT REPLACED RIGHT BANK CAT AND HEATED OXYGEN SENSOR BEFORE CAT. WHAT ELSE COULD BE WRONG?
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2005 Ford Expedition Question: CODE P0420
Answer #1Oakman February 04, 2010, 19:41Master
Did you change the O2 sensor before or after the Cat on your 2005 Ford Expedition? I know of one case (It was a Cadillac) where the rear O2 sensor, the one after the Cat failed in such a way to case a P0420 to set.
Answer #2kisses2kenney26 July 14, 2010, 14:32Rookie
We have same model, same problem. Ever figure it out?