Oxygen Sensor: Description and Operation

^ The Heated Oxygen Sensor (HO2S) compares the oxygen content of the ambient air with the oxygen present in the exhaust gas and generates a voltage signal that becomes an input to the Engine Control Module (ECM).
^ The voltage signal for a rich mixture (low oxygen) is approximately 0.7 - 0.9 volts. The voltage signal for a lean mixture (high oxygen) is approximately 0.0 - 0.3 volts.
^ During the transition for rich to lean and vise versa, a voltage from 0.7 - 0.9 volts to 0.0 - 0.3 volts an back again occurs.
^ Because of the sudden voltage jump, oxygen sensor control can not maintain the ideal mixture composition, (i.e. lambda = constant 1.0). The control fluctuates continuously between "slightly too lean" and "slightly too rich."
^ With warn engine, the control frequency during idle must be at least 0.5 Hz (30 oscillations per minute). At elevated idle speed (2,500 - 2,800 RPM), the control frequency must be at least 1.0 Hz (60 oscillations per minute). One oscillation equals the voltage jump from the highest to the lowest value and then back again to the highest value.

POSSIBLE MALFUNCTIONS:
If the voltage change does not occur, or occurs only slowly, the following malfunctions can be present:
^ Slots or holes in oxygen sensor probe plugged.
^ Sensor is thermally overstressed.
^ Resistance in signal wire and/or reference ground (GND) wire.
^ Sensor too cold; sensor heater not operating.
^ Oxygen sensor control switched OFF (ECM has recognized a malfunction in the fuel injection system; check DTC memory.
^ Sensor was damaged by a terminal cleaning spray or similar. (Terminal spray is drawn into the sensor through the tiny space surrounding the wire strands in the signal wire insulation due to thermal fluctuations and capillary effect).
^ Sensor was damaged by silicon vapors. (Traces of silicone are aspirated by the engine because of the use of sealants containing silicone. Silicone is not consumed during combustion and can damage the sensor).