Oxygen Sensor: Description and Operation

O2 Sensor:

The oxygen (O2) sensors, which are mounted in the exhaust flow, monitor the amount of oxygen in the exhaust gas. The sensor has a close-end tube made of ceramic zirconia. The inner surface of the tube is exposed to atmosphere and the outer surface to exhaust gas. The difference in the quantity of oxygen contacting the zirconia creates electricity. The zirconia tube is coated with platinum to increase it's generating power.
The voltage is approximately 1 volt in richer conditions and approximately 0 volt in leaner conditions. The radical change from 0 to 1 volt occurs at around the ideal air/fuel mixture. The sensor is equipped with a heater element to allow it to operate sooner than if it had to rely on exhaust gas only to heat it to operating temperature.