I'd start by reading the following:
http://www.obd-codes.com/trouble_cod...old-bank-1.php

Then check for the federal warranty on cat converters, etc.
I am not optimistic on the latter, but it's good to know
about it.

Google has a lot of advice on this.



"loub" <ljbuban@yahoo.com> wrote
> I have a 99 Odyssey with 114k miles. At 103k miles the
> MIL came on
> with the codeP0420.I recently had a timing belt service
> done by a Honda
> dealer, they said I needed a new catalytic converter. I
> have been
> driving since 1968 and have favored Hondas. I have never
> needed a cat.
> before and I am starting to lose confidence in Honda's
> supposed "great"
> reliability. Could the cat. really be bad or could it be
> something
> simpler like an oxygen sensor?
>