Oxygen Sensor: Description and Operation

PURPOSE
The Engine Control Module (ECM) uses the Heated Oxygen Sensor (HO2S) signal to correct fuel mixture by changing injector duration as required.

CONSTRUCTION
The sensor uses zirconia and platinum to compare exhaust oxygen content with that of the outside air.

OPERATION
When heated by the combination of its internal heater and exhaust gases, the sensor supplies a low voltage signal (0 - 1 volt) to the 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 lower causing a lower voltage signal to be produced.

The HO2S has a built-in heater which is powered by battery voltage every time the ignition switch is turned on, in order to help in its generating a signal.