FordBum wrote:
Then pulled the 0420 code which is an oxygen sensor. Drivers side, upstream.
  P0420 means ?Catalyst System Efficiency Below Threshold (Bank 1)?.  Ostensibly, this means your bank 1 precat has gone bad and needs to be replaced.  It's possible that this is really an O2 sensor problem, as there is an O2 sensor before and after each precat, used to monitor their condition.  I've been told that EGR problems can cause wonky O2 sensor readings, and it seems to me that this, in turn, could cause the PCM to think the cat's gone bad.  As someone else is going to post some time after this posting, I suggest that you fix your EGR problem first.  BTW, I do not agree with the advice that someone else is going to offer, of cleaning your EGR valve.  I tried that once, and it only solved the problem for a short time.  Given the amount of work involved in removing and replacing the EGR valve, it only really makes sense to remove a questionable valve if you have a new one to install in its place.

  Oh, and one other thing.  It might not be the actual valve at all.  I understand that the Duratec is subject to having the EGR passages become blocked with carbon deposits.  Perhaps someone will post here with instructions for checking and cleaning these passages.

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Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX.  No mods. (Well, OK, one mod.  Before I got rid of my previous car, a 1994 Tempo, I swapped radios.  I liked the Tempo's radio better.  That counts as a mod, doesn't it?  I also kept one of my Tempo's wheels to use as a spare.  I hate those stupid ?compact? spares that come with modern cars.  Does this count as a mod?  If so, I guess I have two mods.  Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)