HO2S(S2) is in the rear side of Catalytic Converter to check the proper operation of catalyst. Oxygen density after the catalytic converter has to be within specific range (around 0.5V when there is no acceclation and deceleration.)
If the oxygen density changes in accordance with HO2S(S1), it means the poor performance of catalytic converter.
If there is not any signal activity, ECM sets DTC P0140.
(This DTC might be caused by the malfunction of Heater circuit, so, check the heater circuit first. )
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Signal no activity detect | 1. Poor connection 2. Open or short in signal circuit 3. S2 |
Enable Conditions |
•
Dew point end detected
•
Battery voltage > 11V
•
Exhaust Gas temperature = 350℃~800℃
•
No upstream O2 sensor heater error
•
Oscillation Test not completed
•
Fuel feed back control active
•
time duration for Target lamba = 0.9 (15sec)
•
Lambda feed back control value = 0.95~1.05
•
Rear O2 sensor heater monitoring - completed | |
Threshold Value |
•
Sensor voltage < 0.65V | |
Diagnostic Time |
•
315 sec | |
MIL ON Condition |
•
3 driving cycle |
※ S1 : upstream oxygen sensor / S2 : downstream oxygen sensor
The amplitude of the signal output of the rear HO2S is small compared to the front HO2S because the rear HO2S detects emission gas purified by the catalytic converter. This is the normal signal waveform of the rear HO2S at idle.
