Most newer cars have multiple O2 sensors. They are now in front of the
converter, and usually after the converter as well. Great care must be
taken with the wiring harness for the sensor, if it touches the hot
exhaust pipes it will melt and ground out, and mess up the reading.
Also the oxygen sensor code can be the result of a bad egr valve, which
may need cleaning or replacement, or a plugged  fuel injector, or bad
pressure regulator, or even a bad air cleaner. I tell everybody with
the newer cars, clean the throttle body of the fuel injector, or have
it done, it is cheap and easy to do, and always use fuel injector
cleaner every third tank of gas. You really should buy a scanner or go
to a parts store like Auto Zone where they will scan your car for free,
and make a reccomendation. Also sometimes the aftermarket O2 sensors
don't work very well, especially the ones from Auto Zone, go figure.