Oxygen Sensor: Description and Operation

View: Typical Heated Oxygen Sensor:

PURPOSE
Measures oxygen content of exhaust gas and sends a coresponding voltage signal to the powertrain control module engine (PCME). The PCME determines air/fuel ratio based on sensor (input) signals and makes appropriate adjustments to maintain the optimum ratio for prevailing operating conditions.

Heated Oxygen Sensor Operation:

OPERATION
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 with a range of approximately 0.1 - 1.0 Volts. 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 PCME. The sensor element only reacts efficiently with oxygen if the temperature of the element is around 300°C (575°F) or hotter.

Electrical heating elements help warm the sensors up to operating temperature more quickly and maintain their temperature during times when the sensors may cool off, such as prolonged idle or deceleration. The heating elements are self-regulating PTC (positive temperature coefficient) heaters. When cold, resistance is low. As the elements warm up resistance increases, reducing current until a steady state of temperature equilibrium is reached. Battery power for the heaters comes from main relay terminal D and enters at sensor terminals C. The other sensor heater terminals are connected directly to ground. The heaters operate continuously while the ignition is ON.


The heated oxygen sensors affect the operation of the following PCME output systems and/or devices:
- Fuel injection quantity
- Purge solenoid valve (purge control)
- Self-diagnosis checker (diagnostic trouble codes)
- Self-diagnosis checker (monitor lamp)

CONSTRUCTION
Sensors consist of hollow zirconia elements with a platinum coating on their inside and outside surfaces. The open ends are exposed to the atmosphere and their surfaces are connected to the PCME. The closed ends protrude into the exhaust stream and their surfaces are connected to ground. The heating elements are self-regulating PTC (positive temperature coefficient) heaters.