Where are the o2 sensors on a 2003 Toyota Highlander?

On a 2003 Toyota Highlander, the oxygen sensors are located in two main areas: one before the catalytic converter (upstream) and one after it (downstream) for each bank of the engine. For the V6 engine, you'll find the upstream sensor on each exhaust manifold, while the downstream sensors are located in the exhaust pipe after the catalytic converter. If you're working on the vehicle, ensure to access them from underneath the car or through the engine bay, depending on their location.