Oxygen Sensor: Description and Operation

PURPOSE
The Heated Oxygen Sensors measures the oxygen content in the exhaust and sends a voltage signal to the ECM.

Two oxygen sensors are used to allow the MPI control module to monitor the oxygen content in each cylinder bank individually.

OPERATION
The Heated Oxygen 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 within a temperature range of approx. 545 - 1530°F (285 - 850°C). It is electrically heated to reach its operating temperature as fast as possible. When the ignition is turned ON, current is sent to the PTC (positive temperature coefficient) resistor (heating stem) whose resistance increases as temperature increases.

Exhaust gases reach the outer surface of the Heated 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.


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


SIGNAL
The sensor signal voltage is in direct proportion to the amount of oxygen in the exhaust gases. This depends on the air/fuel ratio. A "Lambda" value of 1 represents the theoretically perfect ratio. A rich mixture results in a higher voltage than a lean mixture.

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

The voltage produced by the Heated Oxygen Sensor varies between 0.1 - 1.0V. The ECM uses this information to adjust the amount of fuel injected.