Rear Heated Oxygen Sensor

Rear Heated Oxygen Sensor:

OPERATION
The rear heated oxygen sensor (Rear HO2S), downstream three way catalyst, monitors the oxygen level in the exhaust gas. This sensor is made of ceramic titania, the electric resistance of which drastically changes at the ideal air-fuel ratio. The output voltage of the sensor, depending on its resistance, is approximately 0 to 1.5V.
The rear heated oxygen sensor is not directly used to control the engine system. 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, due to the oxygen storage capacity of the up-stream three way catalyst. To judge the malfunctions of rear heated oxygen sensor, ECM monitors the sensor's voltage value and the switching response during the various driving condition such as fuel-cut.