Oxygen Sensor: Description and Operation

PURPOSE AND LOCATION
The oxygen (O2) sensor, mounted in the exhaust flow, monitors the amount of oxygen in the exhaust gas.

CONSTRUCTION
The sensor has a closed tube made of ceramic titania. The inner surface of the tube is is exposed to atmosphere while the outer surface is exposed to the exhaust gas.





OPERATION
The titania in the sensor changes it's electrical resistance drastically at the moment the "ideal" air-fuel ratio is achieved. When the ECM reads a change from the source voltage, the fuel injector pulse width will be modified accordingly.

The ECM will receive between 0 - 1 volt and interpret the voltage as follows:

^ A richer A/F mixture equals higher voltage (Approx. 1 volt).
^ A leaner A/F mixture equals a lower voltage (Approx 0.1 volt).

The ECM also interprets the number of voltage "swings" (cross-counts) and will vary injector open times to control the air-fuel ratio.