For the Toyota RAV4 (2008–2010), the "upstream" sensor is technically an Air/Fuel (A/F) Ratio Sensor. It is located before the catalytic converter and is critical for regulating your engine's fuel-to-air mixture.
Which Sensor Do You Need?
The quantity and type of sensors vary depending on your engine size:
2.4L or 2.5L 4-Cylinder: Uses one upstream A/F sensor and one downstream O2 sensor.
Common Part Numbers: Denso 234-9049, Denso L V6: Uses two upstream A/F sensors (one for Bank 1 and one for Bank 2).
Common Part Numbers: Denso 234-9022, Denso 234-4501