First, a little history. 2005 Outback 2.5i AT wagon 135k miles. I have had the intermittent and recurring P0420 (warning: your catalytic converter is dying/dead) for about 30K miles so, in the interim, I may have already done irreparable damage to the cat(s).
Consensus is that cats don't die, they are killed!
When I first went to the dealer with the code, they said "You need a new cat".
Well, yes that may be but without diagnosis of what caused the damage to the cat, I would need yet another new cat in short order.
Cardoc on subaruoutback.org has an excellent writeup on possible causes: http://www.subaruout...-diagnosis.html
With the use of a $10 VAGCOM OBDII to usb cable and RomRaider free software, I was able to log real time info on my car's performance.
I am attaching the output zip file in the hopes of getting some help in proceeding with a cure for the underlying cause. If you want to follow this, my posting (username - Juicer) starts at #194 at the above link and in addition, off line, Cardoc's analysis of the data warns:
"Check fuel delivery, pressure and check for vacuum leaks if the fuel pressure is good. Bank 1 is on the end of the fuel system, so if fuel flow is low, it will make bank 1 run lean, which is what is happening. The rear O2 sensors all show a lean mix. Find it quick or you'll be buying a couple CATs due to melting."
Soooo, after 2 years and 30K miles after SOA's "recommendation", monkeying around with spacers, new front O2 sensor, and voodoo, there appears to be a LOGICAL DIAGNOSIS of the underlying cause.
There have been so many posts about the P0420 that I hope to be able to collaborate to make this a sticky for those unfortunates who follow.
In the meantime, in my particular case, I need some guidance on how to "Check fuel delivery, pressure and check for vacuum leaks".