Catalytic system reading above threshold (bank 2)
 

04 Sierra 1500 4.8L Check Engine Light is on check with code checker at parts store and it read "catalytic system reading above threshold (bank 2). Everyday for a few days I went back to the store and cleared it. It seems that it only comes on when idling. Any help appreciated from an experienced technican! Thanks in advance

99% of the time the converter is bad