Oxygen Sensor: Description and Operation

Oxygen Sensor Circuit Diagram:

Purpose:
These sensors monitor atmospheric air versus exhaust gas oxygen content to produce a voltage output. This voltage ranges from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture). By monitoring the oxygen sensor output voltage, the computer can determine the amount of oxygen in the exhaust gas and adjust the air/fuel mixture accordingly.

Operation:
The oxygen sensor is essentially a small variable battery, it has the ability to produce a low voltage signal that feeds information on engine exhaust oxygen content to the ECM. Constructed from zirconia/platinum the sensor generates a voltage under certain conditions.

At operating temperature the element becomes a semiconductor. A platinum coating on the outer surface of the element stimulates further combustion of the exhaust gases right at the surface, this helps keep the element up to the desired temperature.

The atmosphere contains approximately 20% oxygen. The oxygen sensor has an inner cavity filled with atmospheric or reference air. The inner cavity acts as the positive terminal while the outer surface protrudes into the exhaust and is connected to ground. Differences in the oxygen concentration reacting with the inner and outer surfaces of the sensor produce small voltages. The ECM monitors the voltage produced and calculates the air/fuel mixture. The ECM continually varies the air/fuel mixture in response to oxygen sensor voltages to maintain the air/fuel ratio as close as possible to the ideal ratio of 14.7:1 by mass.

Location:
An oxygen sensor is located in each side exhaust pipe between manifold collector and catalytic converter.