ses light just came on

[crate]

Last weekend my ses light came on, went to autozone and was P0430. Had them to remove the code to see if it came back, saturday it came back same code which is P0430 Catalyst System Efficiency Below Threshold (Bank 2)

 

 

Searching on here found it either a bad cat on pass side or a bad o2 sensor on the pass side behind the cats, but on the post no one ever gave an update on what it was.

 

I have a 99 gmc 4.8. has 123,000 miles on it, runs fine, still has same power , never had any misfire codes. could htis be just he o2 behing the cat? is there anyways to check the cat without driving to dealer?

 

thanks