97 4.6L O2 sensor(?)s

Hi All.
Are there two O2 sensors on this engine or just one. We got a OBD2 code TCI-P0175 indicating a "rich right bank", and we only saw one O2 sensor.
Any thoughts?
Thnx in advance.

there should be 1 post cat and 1 in the cat, thats all im aware of, may be more