p0420 code replace cats

[crotonevans]

I had a bad cat so I replaced them 2007 Tahoe 80,000mi left the shop and 10 miles got a 0420 code catalyst system efficiency below threshold bank 1
of course they just gave me that info and said good luck look on some sites to find what that all means
I assume bank 1 drivers side
is that just a bad sensor after the converter?
thanks for the help

 

[TheFuzz]

Did they use OEM quality replacements? If you had your cats replaced because one of them went bad, then afterwords you're still getting a CEL related to the cats, I'd be going back to the shop and asking them WTF is going on...

Also, only 80k and a cat goes bad? That's not right. My 02 suburban has 250k on the clock and hasn't needed the cats replaced yet.