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.
ECM checks output signals from HO2S under detecting condition. ECM judges it's signals too slow and sets P0139, if output signal from rear HO2S isn't increased up to specification level within a short time after fuel cut.
(This DTC might be caused by the malfunction of Heater circuit, so, check the heater circuit first. )
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Slow response | 1. Poor connection 2. leak or clog in intake air system 3. Injector 4. Fuel pressure 5. S2 |
Enable Conditions |
•
Dew point end detected
•
Battery voltage > 11V
•
Exhaust Gas temperature = 350℃~800℃
•
No upstream O2 sensor heater error
•
Fuel Cut-off condition
•
Fuel feed back control active
•
integrated air mass during fuel cut-off > 0.62kg ~ 0.78kg
•
Rear O2 sensor monitoring - completed
•
Rear O2 sensor heater monitoring - completed | |
Threshold Value |
•
S2 sensor voltage > 0.15 V | |
Diagnostic Time |
•
2 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.
