It is sensor 1bank 1. Bank 1 is closer to passengers. (Bank 2 is closer to front of vehicle). There are 3 total “oxygen” sensors. Two are pre cat. Literally speaking, the 2 pre cat ones are called”A/F” or air/ fuel sensors but it’s not uncommon to hear them called oxygen sensors and everyone knows what that means. The third one is post cat.
The Bank 1 sensor itself is accessible from under the car. The wire connector connects just underneath the Intake manifold (on the right from above). It can be reached from above or below.
