Oxygen Sensor: Description and Operation

View: 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 controls the air/fuel ratio based on the sensor (input) signal and makes appropriate adjustments to maintain the optimum ratio for prevailing operating conditions.

Heated Oxygen Sensor Operation:

Typical Operation: Voltage vs. Air/Fuel Ratio:

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. The voltage range is 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.

An electrical heating element helps warm the sensor up to operating temperature more quickly and maintain its temperature during times when the sensor may cool off, such as prolonged idle or deceleration. The heating element is a self-regulating PTC (positive temperature coefficient) heater. When cold, resistance is low. As the element warms up resistance increases, reducing current until a steady state of temperature equilibrium is reached. The element gets battery power at terminal C from the ignition switch terminal IG1. The other terminal is connected directly to ground. The heater operates continuously while the ignition switch is ON.

The heated oxygen sensor affects the operation of the following PCME output systems and/or devices:
- Fuel injection quantity
- Purge solenoid valve (purge control)

View: Typical Heated Oxygen Sensor:

CONSTRUCTION
Sensor consists of a hollow Zirconia element with a Platinum coating on its inside and outside surfaces. The open end is exposed to the atmosphere and its surface is connected to the PCME. The closed end protrudes into the exhaust stream and its surface is connected to ground. The electrical heating element is a self-regulating PTC (positive temperature coefficient) heater.