Oxygen Sensor: Description and Operation

Oxygen Sensor (Lambda Sond):

PURPOSE
Under normal conditions, the optimum air/fuel mixture ratio is 14.7kg air to 1kg fuel. The ratio is monitored by measuring the exhaust gas oxygen content. The oxygen sensor senses the oxygen content in the exhaust and sends a voltage signal to the fuel injection ECU.

OPERATION
The oxygen sensor will only operate above a certain temperature, approx. 545°F (285°C). It is electrically heated so that it reaches operating temperature quickly. When the ignition is turned ON, current is sent to the Positive Temperature Co-efficient (PTC) resistor (heating stem) whose resistance increases as temperature increases. This provides a short warm up time and keeps the sensor at the correct operating temperature when the exhaust gas temperature is low.

Oxygen Sensor (Lambda Sond) Voltage Vs. Exhaust Oxygen Content:

SIGNAL
The oxygen sensor produces a voltage signal proportional to the oxygen content in the exhaust gases. This depends on the air/fuel ratio. A "Lambda" value of 1 represents the theoretically perfect ratio. A rich mixture produces a high voltage, while a weak mixture produces a low voltage.

The voltage produced by the oxygen sensor varies between 0.1 - 1.0V. The fuel injection ECU uses this information to adjust the amount of fuel injected.