Where is locations for Toyota Sienna bank 1 sensor 1?

Answer 1

Bank 1 Sensor 1 is on the rear of the engine near the firewall on the rear manifold.

Note that there are three sensors, Bank 1 Sensor 1, Bank 2 Sensor 1, and Bank 1 Sensor 2. There is only one "Sensor 2", that is Bank 1 Sensor 2 and it is under the car by the catalytic converter. There are two "Sensor 1's", one on the front manifold and one on the back manifold. The Bank 2 Sensor 1 is easy to see from above - you open the hood, look at the front manifold, and there it is! However Bank 1 Sensor 1 is a royal pain. I can only see it in my 2000 Sienna from beneath, and though you can see it, it takes skinny arms, long reach, and some effort to get a wrench on it. If it pops free, then it is relatively straight forward to remove it. However if it is stuck (as often happens since they get carbon build-up on the threads inside the manifold) they are a god-awful pain to get out.

Good luck!