[Fireplug]

You have a left bank on the left exhaust manifold, right bank on right exhaust manifold near the bottom of the pipe and precat o2 sensor and some had a post cat o2 sensor.
Just because you get a o2 code does not mean it bad.
You have to check why is it running rich .bAD INJ, BAD SPARK PLUG OR WIRE, o-2 most cases dont just go bad there is something else wrong that kills the o2.
Bank 1 sensor 1 in on the driverside exhaustmanifold
Fireplug