I have a cat code P0420 in a 99 Civic VP with 120k miles. I understand there is a 8yr/80kmile mile warranty on this.

How likely is it to be the cat? I see things in other areas like ODB sensors, o2 sensor, clogged injection system, clogged egr port. (i have not checked any of these things. How likely is it to be these?

Thank you

KieranMullen
http://360oregon.com

In my original visit with the Wizard, my new name for the Prince, I was able to see the actual Honda diagnostics program run on a laptop for a check of my O2 sensors. I have had the P0420 code for about a year now and this was my opportunity to learn if it was really the cat or if I had a chance to just replace the O2 sensors to rid the CEL.
Prince showed me how first the O2 sensors showed they were working by actually providing readings on the exhaust as they should. Then, he pointed out how the values were virtually the same for both sensors. Since the cat is between these, the latter sensor should show a decrease as a result of a properly working cat. Since mine were the same, my cat was indeed no longer working as it should.
The bad news is I need to replace the cat. The good news is I haven't replaced other parts making sure of that fact.
A good tech should provide the same diagnostics for you for $100 or less. May be a good investment to assure what is really wrong.