Oxygen Sensor: Description and Operation

Heated Oxygen Sensor:

Purpose:
The oxygen sensors, installed in the exhaust on each side of the engine just ahead of the catalytic converters, monitor exhaust gas oxygen content and produce a voltage output. The ECM uses this voltage value to calculate the percentage of oxygen in the exhaust gas and adjusts the fuel injector pulse width to maintain the correct air/fuel ratio. This voltage ranges from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture).

CONSTRUCTION AND OPERATION
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 ECM, while the closed end protrudes into the exhaust stream and its surface is connected to ground.

The oxygen sensor element only reacts efficiently with oxygen if the temperature of the element is around 300~C (575~F) or hotter. A cold sensor is like an open circuit and produces no voltage. When there is a difference in the amount of oxygen reacting with the inner and outer surfaces, a voltage potential is generated. The normal operating 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.

A heating element is built into the sensor to help bring it up to operating temperature more quickly, and to help maintain operating temperature during periods when the sensor may cool, such as prolonged idle or deceleration.