o2/cat 16805 update - interesting......
 

I'v had a 16805 bank 1 warm up cat / 17521 bank 1 int reses to large / 17539 bank 2 int reses to large

so, I replaced the first set of 02's....this cleared the 17521 and 17539.... but I still had the 16805....so I decided to swap (per a suggestion) the rear 02s.....interested.....i got 16815 bank 2 warm up cat - so I'm thinking its the 02 sensor and not the cat....but I also got a new cod 17584 - bank 1 lambda correction downstream of catalyst contol limit attained....what the heck is this? tx, jeff

Sounds like the sensor downstream of Cat 1 currently, is bad -
 

or cat 1 is bad. Or both those sensors are bad. Wierd.

Sorry, just realised how useless my post above is!

Hmm, sounds familiar.
 

I'm getting the same code on my S4. I have done nothing to troubleshoot yet, so I'm really interested to see what you come up with.
Would it help either of us if I had mine smogged? Maybe that would rule out a bad cat?
Mine:
16815 - Warm Up Catalyst; Bank 2: Efficiency Below Threshold
P0431 - 35-10 - - - Intermittent

strange how two different codes are both related to the o2 sensors...

I passed smog with my code.
 

I figured that I had a bad cat, but now I guess not.