Oxygen Sensor: Description and Operation

Oxygen Sensor:

Oxygen Sensor:

Oxygen Sensor Operation:

An oxygen sensor is installed in the exhaust manifold where it can monitor the oxygen content of the exhaust gas. The ECU determines air/fuel ratio based on the voltage signal from the oxygen sensor, and makes appropriate adjustments to maintain the optimum ratio of 14.7:1.

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 the atmosphere and its surface is connected to the ECU, while the closed end protrudes into the exhaust stream and its surface is connected to ground. Oxygen reacts with the platinum surfaces when the 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).

Oxygen Sensor Output Voltage vs. 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 oxygen sensor element only reacts efficiently with oxygen if the temperature of the element is around 300~C (575~F) or hotter. An electrical heating element is incorporated into the oxygen sensor to help warm it up to operating temperature more quickly and maintain its temperature during times when the sensor may cool off, such as prolonged idle or decelerating.