Oxygen Sensor: Description and Operation

PURPOSE
Two oxygen sensors, a main and a sub, measure the oxygen content in the exhaust and send a voltage signal to the engine control module (ECM).

CONSTRUCTION
Each sensor consists of a steel housing, sensor tip, its protective sleeve and an internal heating element. The sensor tip itself is made from a platinum covered zirconium-oxide pipe.


OPERATION
This sensor produces a measureable voltage by comparing the amount of oxygen in the exhaust gas with the amount in the ambient air.
The sensor operates only within a certain temperature range of approx. 285 - 850°C (545 - 1530°F).
The exhaust gases reach the outer surface of the oxygen sensor tip via the openings in the protective sleeve. Ambient air reaches the sensor's inner surface via channels. The differance in oxygen content produces a voltage read by the ECM.

Schematic View Of Oxygen Sensors Circuits:

The heating element is controlled by the ECM. When the sensor is cold the ECM grounds the circuit, causing the sensor to heat. The electric heater allows the sensor to reach operating temperature much sooner than it could simply by using exhaust gas to heat it. The heater also prevents sensor cool-down during periods of extended idling.