Oxygen Sensor: Description and Operation

Oxygen Sensor (Lambda Sond):

PURPOSE AND LOCATION
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. The oxygen sensor is mounted in the exhaust manifold about 15cm (6in) in front of the catalytic converter.

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

OPERATION
This particular model of oxygen sensor is known as a "comparing oxygen sensor". It 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). 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.
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 ECU.

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

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 then a lean mixture. 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.