Where is the oxygen sensor located on a 2000 Toyota Sienna?

On a 2000 Toyota Sienna, the oxygen sensor is typically located in the exhaust system. There are usually two sensors: one upstream (pre-catalytic converter) and one downstream (post-catalytic converter). The upstream sensor is generally found on the exhaust manifold or just after it, while the downstream sensor is located before the exhaust pipe exits the catalytic converter. For precise location, it's best to consult the vehicle's service manual.