Oxygen Sensor: Description and Operation

Oxygen Sensor:

PURPOSE
The oxygen sensor is installed in the exhaust manifold to monitor exhaust gas oxygen content. The ECU determines air/fuel ratio based on sensor voltage signal and makes appropriate adjustments to maintain the optimum air/fuel ratio.

LOCATION
Exhaust manifold near exhaust pipe flange.

OPERATION

Oxygen Sensor Operation:

Oxygen Sensor Output Voltage vs. Air/Fuel Ratio:

Oxygen reacts with the platinum surfaces when temperature is high. When there is a difference in the amount of oxygen reacting with the inner and outer surfaces, a voltage potential is generated. The voltage range is approximately 0.1 - 1.0V. Voltage increases when the concentration of oxygen in the exhaust is low (rich air/fuel ratio) and decreases when the concentration is high (lean air/fuel ratio). The difference in oxygen concentration in the narrow range of optimum air/fuel ratio causes a large voltage change that is easily measured by the ECU.

The sensor element only reacts efficiently with oxygen if element temperature is around 300°C (575°F) or hotter.

CONSTRUCTION

Oxygen Sensor:

The sensor consists of a hollow zirconia element with a platinum coating on its inside and outside surfaces. The open end of the element is exposed to atmosphere and its surface is connected to the ECU. The closed end protrudes into the exhaust stream and its surface is connected to ground.