Oxygen Sensor: Description and Operation

Heated Oxygen Sensor 2 (Rear)







COMPONENT DESCRIPTION
The heated oxygen sensor 2 (rear), after TWC (Manifold three way catalyst), monitors the oxygen level in the exhaust gas. Even if switching characteristics of the air fuel ratio (A/F) sensor 1 are shifted, the air fuel ratio is controlled to stoichiometric, by the signal from the heated oxygen sensor 2.

This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1 V in richer conditions to 0 V in leaner conditions.

Under normal conditions the heated oxygen sensor 2 (rear) is not used for engine control operation.

Heated Oxygen Sensor 2 (Rear) Heater




SYSTEM DESCRIPTION
The ECM performs ON/OFF control of the heated oxygen sensor 2 heater (rear) corresponding to the engine speed.

Heated Oxygen Sensor 3







COMPONENT DESCRIPTION
The heated oxygen sensor 3, after ADS-TWC (Adsorber pre-catalyst), monitors the oxygen level in the exhaust gas.

This sensor is used for recovery control of air fuel ratio after the fuel cut operation.

This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1 V in richer conditions to 0 V in leaner conditions.

Heated Oxygen Sensor 3 Heater




SYSTEM DESCRIPTION
The ECM performs ON/OFF control of the heated oxygen sensor 3 heater corresponding to the engine speed.

Air Fuel Ratio (A/F) Sensor 1







COMPONENT DESCRIPTION
The A/F sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the element.

The sensor is capable of precise measurement lambda = 1, but also in the lean and rich range. Together with its control electronics, the sensor outputs a clear, continuous signal throughout a wide range (0.7 < lambda < air).

The exhaust gas components diffuse through the diffusion gap at the electrode of the oxygen pump and Nernst concentration cell, where they are brought to thermodynamic balance.

An electronic circuit controls the pump current through the oxygen - pump cell so that the composition of the exhaust gas in the diffusion gap remains constant at lambda = 1. Therefore, the A/F sensor is able to indicated air/fuel ratio by this pumping of current. In addition, a heater is integrated in the sensor to ensure the required operating temperature of 700 - 800 °C (1,292 - 1,472 °F).

Air Fuel Ratio (A/F) Sensor 1 Heater




SYSTEM DESCRIPTION
The ECM performs ON/OFF duty control of the A/F sensor 1 heater corresponding to the engine operating condition to keep the temperature of A/F sensor 1 element at the specified range.