This car has had the CE light on and off for a while. I been chasing symptoms a few months.

A few weeks ago we had a code pointing to the O2 behind the cat as bad. I had it replaced and no CE light for about 3 weeks.

Now I have the dreaded P0420 bad catalyst code. Before I go and change the cat is there anything else could be causing this code?

The car has to be NYS inspected by the end of the month so I do need to clear this up soon.