P0420 is a catalyst system low efficiency

Question - I've had this code pop up every now and then; sometimes it clears itself and other times I clear it by clearing all codes. Can anyone shed some light on what triggers it? Is it a catalytic converter problem? At this point, I'm not too worried about it but I thought I'd ask you experts.

 

P0420 occurs when pre and post cat.conv. O2 sensors data indicates cat conv performance is below what would pass emission test as analyzed by PCM.

 

Thanks for the info Slowroll...since we don't have to pass an emissions test here, I'm not going to worry about it unless I see a degradation in the car's performance.