Oxygen sensor

How Does An Oxygen Sensor Work In An Engine?

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What Is An Oxygen Sensor?

Technically, oxygen is very important for an engine. It determines the proper engine performance. So, to achieve the correct air-fuel ratio manufactures employ oxygen sensors in the exhaust systems. Besides, the exhaust gas oxygen sensor is also known as the ‘lambda sensor’. It is located before the catalytic converter in the exhaust pipe. The sensor generates a voltage with regards to the amount of oxygen in the exhaust gas. Thus, it provides real-time feedback on the mixture composition to the engine management system.

Bosch O2 sensor
Bosch O2 sensor

Furthermore, the engine management system (EMS) is calibrated. It provides optimal engine power, emissions and economy over the entire engine operating range. The oxygen sensor helps the EMS to monitor the optimal emission in the exhaust system. Thus, it achieves the ideal air-fuel ratio of 14.7:1.


Furthermore, the oxygen sensor consists of a ‘galvanic cell’ battery. The sensor contains two porous platinum electrodes. Besides, they have a ceramic electrolyte (Zirconium Dioxide) between them. The oxygen sensor generates a voltage. It ranges from as little as 100mV (0.1 volts) up to a maximum of 900mV (0.9 volts). This depends upon the oxygen level in the exhaust gases. The oxygen sensor compares atmospheric oxygen, typically 21% approx., to the amount of oxygen in the exhaust.

O2 Sensor
O2 Sensor (Courtesy: Denso)

Typically, a rich mixture contains more fuel per part of oxygen. This means it has 0% oxygen. So, the sensor produces a high voltage of around 900mV. A lean mixture has less fuel per part of oxygen. It may contain 3% to 4% of oxygen. So, the sensor produces a low voltage of 100 mV. However, the average voltage of the sensor is ~ 450mV which results in the ideal mixture ratio of 14.7:1.


Rich Mixture - large difference between atmospheric and exhaust oxygen levels. This results in high conductivity between the electrodes. Hence, the voltage output is high at around 900mV.

Lean Mixture - the smaller difference between oxygen levels. This results in less conductivity and smaller voltage output, typically around 100 mV.

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