Due to possible oxygen sensor defects (e.g. reference air poisoning) or faults in the injection system (e.g. leaking fuel injector), the rear oxygen sensor may not provide the expected lean or rich signal level during fuel cut-off or full load condition. Hence, the oxygen sensor signal is checked for plausibility during this engine operating states.There are 2 cases which DTC P0140 sets. (I) Signal monitoring during fuel cut-off: The PCM/ECM monitors rear O2 sensor signal level during fuel cut-off which normally shows near 0V and sets DTC P0140 when signal level is too high. (II) Signal monitoring after fuel cut-off: The PCM/ECM monitors rear O2 sensor signal level after leaving fuel cut-off and sets DTC P0140 when signal remains at or below 0.6V.
Item | Detecting Condition | Possible Cause | |
DTC Strategy | Case 1 |
•
Signal plausability with rich mixture (during catalyst purge after fuel cut-off) | 1. Poor connection or damaged harness 2. HO2S contamination |
Case 2 |
•
Signal plausibility with lean mixture (during fuel cut-off) | ||
Enable Conditions | Case 1 |
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Coolant temperature >73℃(163℉)
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Downstream O2 sensor operative readiness detected
•
Downstream O2 sensor pre-heating phase finished
•
4g < Integrated Mass Air Flow in last Fuel Cut-Off
•
Downstream O2 sensor signal at end of last fuel cut off <0.3V
•
Integrated air mass flow in Part Load >150g
•
Minimum upstream O2 sensor voltage during Catalyst Purge phase >0.6V
•
Modelled catalyst temperature >400℃(752℉)
•
No relevant failure
•
11V< Battery voltage <16V | |
Case 2 |
•
Downstream O2 sensor operative readiness detected
•
Downstream O2 sensor pre-heating phase finished
•
12g < Integrated mass air flow since fuel cut-off begin <250g
•
No relevant failure
•
10V< Battery voltage <16V | ||
Threshold Value | Case 1 |
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Max. downstream HO2S <0.6V during catalyst purge after fuel cut-off | |
Case 2 |
•
Downstram HO2S >0.3V during fuel cut-off phase | ||
Diagnostic Time | Case 1 |
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3 valid fuel cut-off followed by catalyst enrichment phases | |
Case 2 |
•
5 sec. | ||
MIL On Condition |
•
2 Drive Cycles | ||
