Well I just replaced my bank 1 o2 sensor and it was on the passenger side, so I assume the bank 2 would be on the driver side (the front one that goes into the header).
Very well could be the back one on yours, I forget which one does what. My front one went bad and was causing a seriously rich condition (bad enough to load up the engine). If it was on a scan tool they coulda/shoulda told you which one it was. Easy way to tell is to pull it out, hold the washer firmly in place and shake the sensor. If you hear it rattle, it's bad.