P420 code but no symptoms/indications otherwise of bad converter

[yabadabadoo1026]

Have a 2001 Volvo s60----not the turbo---and getting this code from the code reader at Autozone----took it to a mechanic who hooked it up to his computer software and he confirmed converter is bad. This car has but 130,000 on it and has no symptoms at all of bad cat--- its running good, no misses, no sluggishness, no restriction / good blow out the tailpipe, no smoke, no rotten egg smell. Any thoughts if there can be anything else causing this code to pull. I know oxygen sensors can inter-relate a bit with cats BUT I know there are codes that tell you if you have a a bad O2 since I've had such in past and put a new upstream in. Since getting no O2 codes suspect spending $$ on replacements would just be a waste that wont fix the 420 keeping me from passing emissions

If the car was running bad or showed symptoms id bite the bullet and put a cheaper aftermarket universal cat in it. Since its running good with no symptoms tempted to try the cheap downstream O2 hack so many Youtube vids on to fool the puter that the cat is ok.

Any thoughts if this might be a false code triggered by something else wrong ( though the mechs software also said its bad)-------at 130000 mile and running good just have a hard time believing it