For 2.8 ATQ there is an ECU software update that raises the o2 sensor threshold. (I thinhk there might have been one on 2.7T too.) The factory threshold was set too low and was triggering P0421 and P0431 codes even though the catalytic converters and 02 sensors were in decent conditions. Ask the dealer to update the ECU to the latest version if yours is not already. It usually (but not always) gets rid of the warm up catalyst codes. Bad thing is that I had to pay amout $300 to do the update.