Heated Oxygen Sensor (HO2S)
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2003 Lexus SC 430, 2003 Lexus RX 300, 2003 Lexus LX 470, 2003 Lexus LS 430, and 2003 Lexus IS 300. However, it is still accessible from the selected car via links, so may be relevant.
HO2S monitors exhaust gas oxygen content and generates a voltage signal that ECM uses to determine fuel injection duration. HO2S is heated by an electric heater element.