Originally Posted by mnstrmech
actually, being an ASE technician for the last 10 years, a p0420 IS a dead cat, 99.99% of the time. ......
I disagree, even though I am not a certified mechanic.
On Subarus at least, 90% of the time it's a bad front O2 sensor and those who frequent this forum who have had this issue can add their own 2 cents.
I personally have had 4 different Subys which have had this code come up and in every case it was resolved with a new front sensor.
Now if you continue to run with it, you may start to burn rich, which will eventually ruin a cat.