Upstream & Downstream Heated Oxygen Sensors
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2002 Mercury Sable, 2002 Mercury Mountaineer, 2002 Mercury Grand Marquis, 2002 Mercury Cougar, and 2002 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
Heated Oxygen Sensors (HO2S) provide PCM with voltage and frequency information related to oxygen content of exhaust gas. For additional HO2S information, see HEATED OXYGEN SENSOR under PCM INPUTS under COMPUTERIZED ENGINE CONTROLS. In addition to providing PCM with indications of how rich or lean the engine is operating, upstream HO2S signal serves as an input to HO2S monitor. Downstream HO2S signal is an input to Catalyst Efficiency Monitor. For additional Catalyst Efficiency Monitor information, see CATALYST EFFICIENCY MONITOR DESCRIPTION under DIAGNOSTIC MONITORS under COMPUTERIZED ENGINE CONTROLS.