Got a check engine light on my 2001 Volvo V70 T5 this weekend and swung by a Autozone for a free OBD reading and they told me it was code PO0422 I found this online

PO422 Main Catalyst Efficiency Below Threshold Bank1

The Car seems to drive fine but not sure if that would likely mean my O2 sensor is bad or the cat itself. I called up my Volvo Dealer and gave them the code, and was told VOLVO uses their own code system and they could not tell me what was wrong without paying $120 diagnostics fee.

I'm currently laid off and obviously would like to save money if I can. Also if it is the cat would you guys recommend any aftermarket cats because a Volvo one costs 1K Also I have to pass Illinois emissions in the next few weeks, is there a way to clear the code myself?

 

A generic 0442 code equates to a volvo code EFI-612 "small leak, intermittent fault" which is an evap fault. The most common cause is fuel filler cap, maybe a hose in the evap system.
I would see if autozone would clear it and hope it doesn't come back (many intermittent evap codes don't.