Oxygen Sensor: Description and Operation

Fig. 57 O2 Sensor:

PURPOSE
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.

O2 Sensor Operation:

OPERATION
The titania in the sensor changes it's electrical resistance drastically at the moment the "ideal" air-fuel ratio is achieved. When the Engine Control Module (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.