Rear Heated Oxygen Sensor

DESCRIPTION




The rear heated oxygen sensor (Rear HO2S), after the three way catalyst, monitors the oxygen level in the exhaust gas.
Even if the switching characteristics of the front heated oxygen sensor shift, the air-fuel ratio is controlled to stoichiometric by the signal from the rear heated oxygen sensor.
The 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.
Under normal conditions, the rear heated oxygen sensor is not used for engine control operation.
It is used only for the on board diagnosis of three way catalyst.

ON BOARD DIAGNOSIS LOGIC




The rear heated oxygen sensor has a much longer switching time between rich and lean than the front heated oxygen sensor. The oxygen storage capacity before the three way catalyst causes the longer switching time. To judge the malfunctions of rear heated oxygen sensor, ECM monitors the sensor's voltage value and the switching response during the various driving conditions such as fuel-cut.