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.
In case the sensor output is 0.4~0.52 V during 600sec or the internal resistance is over 40 ? under enable conditions, ECM sets DTC P0136. ( 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, wiring interruption
Poor connection
Open or short in signal circuit
S2
General
Enable
Conditions
After enough heated
Battery voltage > 10.7V
Catalyst temperature (model) : 350°C ~ 800°C
Case1
ThresholdValue
Sensor voltage : 0.4~0.52 V
DiagnosticTime
600 sec
Case2
Catalyst temperature (model) > 600 ?
Internal resistance > 40 ?
MIL ON Condition
3 driving cycle
? S2 : 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.