I hope this is the right place to post.

Just got my '96 Civic HB scanned cuz of a Check Engine Light and the code came out as PO420 (Catalytic Converter Below Threshold). The tech suggested a swap of my cat--I informed him that I just passed smog 2 months ago.

Question: could the code be referring to a simpler (and cheaper) problem such as an O2 sensor? Or am I SOL and gonna have to pay up for a new cat? Anyone have experience with this before?

Thanks in advance.