2009 CTS4 3.6L

P0430 catalyst below efficiency bank 2 comes on periodically. (There are no other codes being thrown.)

I put a data logger on it today on my drive to work and the rear sensor is certainly erratic at times. It doesn't necessarily follow the front sensor signal.

I thought the most reasonable way to test it would be to swap the sensors side to side. Then if the problem follows the sensor, it's the sensor that is bad. If the problem stays on the driver side, it's the catalytic converter that has gone bad.

However, due to the placement on the driver side, the entire pipe has to come down to access it. As I've just had twin daughters, my time for repairs is minimal and if I'm going to drop that pipe I want to only do it once.

Is there any way I can conclusively determine if it is the sensor or converter prior to removing anything?