Oxygen Sensor: Description and Operation

Oxygen Sensor Location:

The oxygen (O2) sensor, which is mounted in the exhaust manifold, monitors the amount of oxygen in the exhaust gas. The sensor has a closed tube made of ceramic zirconia.

Oxygen Sensor:

The inner surface of the tube is is exposed to atmosphere while the outer surface is exposed to the exhaust gas. The differences in oxygen content makes the sensor generate an electrical current. To enhance the generating capacity of the zirconia, the tube is coated with platinum.
A richer A/F mixture equates to a higher voltage (approx. 1 volt).
A leaner A/F mixture equates to a lower voltage (approx 0.1 volt).

Oxygen Sensor Voltage:

The ECU interprets the voltage change as the stoichiometric point and will attempt to control the injector duration, ignition timing and several other systems to maintain that condition.