Plugged in the programmer I got from Checker and I have two codes (my SES light is on which is why I got it).
P0420 Catalyst System Efficiency Below Threshold ( Bank 1)
P0430 Catalyst System Efficiency Below Threshold ( Bank 2)
From my understanding from browsing is it looks like it's either the 02 Sensors or a problem with the Cat itself.
Question is, can I easily verify which one is causing the problem by myself and what can I do to fix if it's either one?