My understanding is bank 1 (drivers side) sensor 2 second sensor downstream.
Now as far as the light going out, and then coming back on 2 weeks later, i dunno why 2 weeks. Likely would have gone out in the first place because something changed, so it reset, and then realized, Crap same thing is still happening. But usually after a driving cycle the light should come back on (if it is going to)
Now this is USUALLY. We have had countless times here where we have driven a customers vehicle all over, we have had a tech drive the vehicle home, on and on and on, and no light comes back. So we release to the customer, they phone us about 2 hours later. "My Engine Light Came On As Soon as I Left Your Lot"
So why it took two weeks i don't know.