Catalyst bank 1 under threshold

[EMB1528]

CEL went on and I had it checked and it said that the catalyst bank 1 was under threshold. Can anyone tell me where to start?
-New 02 sensor?
-Fuel Injector cleaner?
-New cat?

I just replaced both gaskets, cop's, and plugs.

 

[97stscaddy]

Sounds like you need a new catalytic converter. I forget which bank is on which side, but might as well do them both. If one is bad the other will likely soon follow.