Oxygen Sensor: Description and Operation

PURPOSE
The Heated Oxygen Sensor (HO2S), located at the exhaust manifold or pipe with the sensor end extending into the exhaust stream, supplies a voltage signal to inform the Programmed Fuel Injection Electronic Control Module (PGM-FI ECM) of the air/fuel mixture in the engine.

OPERATION
The HO2S sensor uses zirconia and platinum to compare exhaust oxygen content with that of the outside air. When heated by the combination of its internal heater and exhaust gases, the sensor supplies a low voltage signal (0 - 1 volt) to the PGM-FI ECM. When the engine is running rich, the oxygen differential is relatively high so signal voltage increases. When a lean condition occurs the difference in oxygen content is much lower causing a lower voltage signal to be produced.