The rear heated oxygen sensor is mounted on the rear side of the Catalytic Converter (warm-up catalytic converter) or in the rear exhaust pipe, which detects the catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0V and 1V. This rear heated oxygen sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.
If the change of the rear HO2S signals is less than 0.3V during driving condition and fuel-cut, the PCM determines that a fault exists and a DTC is stored.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Circuit voltage is monitored when air/fuel is made to be rich by 15% during 10sec. | ● Poor Connection ● Air leakage ● Short to ground in HO2S circuit ● Faulty HO2S ● Faulty PCM |
Enable Conditions | ● Engine coolant > 81℃ | |
Threshold value | ● Front HO2S circuit voltage >= 0.5V, | |
● Rear HO2S circuit voltage < 0.1V, | ||
● Change in rear HO2S circuit voltage < 0.078V | ||
Diagnosis Time | ● Continuous |
