I apologize up front, but the search didn't really answer my question. I only recently started getting P2A00 codes with the CEL/MIL/SES light. I replaced the passenger-side (right side) pre-cat a/f sensor and am still getting the code. I want to confirm that B1S1 is in fact the right side sensor and ask if there are any checks I should do besides the long process in the FSM.

Any help is appreciated.

Thanks

I can't remember which bank they call which, but S1 should definitely be the pre-cat sensor. Do they outline that somewhere in the FSM?
Can you switch that new sensor over to the other side and re-install your old sensor (or replace it as well)?

For the future, the code is the SYMPTOM not the cause. Sometimes they are the same, but not always.

The code P2A00 tells us the ECU thinks bank 1 is too lean (too much O2) in the exhaust.
Bank 1, is the passenger side.

To trouble shoot this effectively, some kind of a ODB scanner (like ELM327 & a phone app) will help you very much. With that you can check your fuel trims live data to understand what the issue is.

If you don't have one, you can try spraying brake clean / starter fluid / unlit propane torch by the intake manifold. If the engine speeds up, you have a vacuum leak.