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 is able to detect 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.
The PCM monitors rich-lean switching time of rear heated oxygen sensor (HO2S) after fuel cut-off to validate dynamic behavior of rear heated oxygen sensor (HO2S). After detection of fuel cut-off engine operating state, the PCM measures rich-lean switching time of the rear heated oxygen sensor (HO2S) signal and compares it to the predetermined limit value. DTC P0139 is set when the switching time is bigger than the limit value.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Slow response(Switching time check at entry in fuel cut off) | 1. Leak in intake or exhaust system 2. Faulty fuel system 3. Front and rear HO2S connections reversed 4. Poor connection or damaged harness 5. HO2S contamination |
Enable Conditions |
•
Coolant temperature >73℃(163℉)
•
Downstream O2 sensor readiness detected
•
Downstream O2 sensor pre-heating phase finished
•
400℃(752℉)< Catalyst temperature model
•
0.6V< Downstream O2 sensor signal at entry into fuel cut-off
•
No relevant failure
•
11V < Battery voltage < 16V | |
Threshold Value |
•
Average ratio between measured and maximum allowed rich to lean switching time entering fuel cut-off >1 | |
Diagnostic Time |
•
4 valid fuel cut-off phases | |
Mil On Condition |
•
2 Driving Cycles |
▶ Sector A : Signal Normal
▶ Sector B : Signal Fluctuation
▶ Sector C : Signal Recovery
