Heated Oxygen Sensors (HO2S)
WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
The HO2S provide the powertrain control module (PCM) with voltage and frequency information related to the oxygen content of the exhaust gas. Refer to the POWERTRAIN CONTROL MODULE (PCM) INPUTS for a description of how the HO2S operates.