Gonna go out on a limb and say bank 1 is the driver's side. This is the defacto bank 1 side for most (all?) engines. Next, I'll suggest you have a bad O2 sensor on that side. Of course, if I provided incorrect advice on which side is bank 1, you could always swap the old (removed) O2 sensor into the passenger side.

There should be an O2 sensor near (or in?) each Catalytic converter. Start by replacing the driver's' side O2 sensor.

https://www.youtube.com/watch?v=WbpQMX5orqY