The normal operating temperature of the HO2S(Heated Oxygen Sensor) ranges from 350 to 850?(662 to 1562?). The HO2S heater greatly decreases the amount of time required for fuel control to become active. The PCM provides a pulse width modulated control circuit to adjust current through the heater. When the HO2S is cold, the value of the resistance is low and the current in the circuit is high. On the contrary, if the temperature in the resistor of the sensor rises, the current drops gradually.
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 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 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
case1
Signal Plausability with Rich mixture (during Catalyst Purge after Fuel Cut-off)
Related fuse blown or missing
Poor connection or damaged harness
HO2S contamination
case2
Signal Plausibility with Lean mixture (during Fuel Cut-Off)
Enable
Conditions
Integrated mass air flow in last fuel cut off > 10g
Integrated mass air flow in part load > 250g
Downstream HO2S sensor signal at end of last fuel cut off < 0.25V
Minimum HO2S(S1) during Catalyst Purge phase < 0.5V
Catalyst temperature > 348?(658?)
No relevant failure
11V < Battery voltage < 16V
20g < Integrated mass air flow since begin
10V < Battery voltage
Fuel Cut Off active
Fuel cut off phase
Threshold Value
Voltage <0.55V
Voltage with fuel cut > 0.1V
Diagnostic Time
3 valid fuel cut-off phases
2 sec.
Mil On Condition
2 Driving Cycles
Test Condition
GDS Parameter
HO2S SNSR VOL.-B1/S1
HO2S SNSR VOL.-B1/S2
Normal Value when
circuit is normal
Idle after warm up
Signal is switching from rich(above 0.45V) to lean(below 0.45V) a minimum of 3 times in 10 seconds.
above 0.7V
HO2S(B1S1) signal circuit open
Approx. 0.43~0.45V
-
HO2S(B1S2) signal circuit open
Fig.1) HO2S signal waveform with idle after warm up :
1: Normal status(Approx. above 0.7V), 2: Open in signal circuit(Approx. 0.4~0.5V)