Oxygen Sensor: Description and Operation

COMPONENT DESCRIPTION







Front HO2S
The front heated oxygen sensor is placed into the exhaust manifold. It detects the amount of oxygen in the exhaust gas compared to the outside air. The front heated oxygen sensor has a closed-end tube made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions. The front heated oxygen sensor signal is sent to the ECM. The ECM adjusts the injection pulse duration to achieve the ideal air-fuel ratio. The ideal air-fuel ratio occurs near the radical change from 1V to 0V.




Rear HO2S
The rear heated oxygen sensor (Rear HO2S), after three way catalyst, monitors the oxygen level in the exhaust gas. Even if switching characteristics of the front heated oxygen sensor are shifted, the air fuel ratio is controlled to stoichiometric, by the signal from the rear heated oxygen sensor. 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 rear heated oxygen sensor is not used for engine control operation.

SYSTEM DESCRIPTION

Operation:

Front HO2S Heater
The ECM performs ON/OFF control of the front heated oxygen sensor heater corresponding to the engine speed.

OPERATION:

Rear HO2S Heater
The ECM performs ON/OFF control of the rear heated oxygen sensor heater corresponding to the engine speed.