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 the sensor output is over 1.08 V under enable conditions, ECM/PCM sets DTC P0138.
(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 check, high | 1. Poor connection 2. Short to power in signal circuit 3. S2 |
Enable Conditions |
•
Dew point end detected
•
Battery voltage > 11V
•
Exhaust Gas temperature = 662℉~1472℉
•
No upstream O2 sensor heater error | |
Threshold Value |
•
S2 sensor voltage > 1.08 V | |
Diagnostic Time |
•
5 sec | |
MIL ON Condition |
•
2 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.
