Caprice V8-265 4.3L VIN W MFI (1995)
Oxygen Sensor: Description and Operation
HO2S Cutaway
Oxygen Sensor Element
The Heated Oxygen Sensor (HO2S) is essentially a small variable battery; it has the ability to produce a low voltage signal that feeds information on
engine exhaust oxygen content to the Powertrain Control Module (PCM).
The PCM sends a reference signal of 450 mV. The reference signal serves to run the engine when it is in "Open Loop" mode of operation. When the
air/fuel ratio is correct the PCM displays 450 mV. When the engine is operating with a rich air/fuel ratio, there is a reduction of free oxygen in the
exhaust stream and the oxygen voltage rises above the reference voltage.
The HO2S is constructed from a material (zirconia/platinum) that conducts electricity under certain conditions. At operating temperature, 315°C (60o°
F), the element becomes a semiconductor. A platinum coating on the outer surface of the element stimulates further combustion of the exhaust gases right
