The heated oxygen sensor 2 (H02S-2) is an electrical source that responds to oxygen content out of the catalytic converter. When the sensor reaches approximately 316°C (600°F), it produces a voltage based on the difference in oxygen between the atmosphere and exhaust gas. The powertrain control module (PCM) sends a bias voltage (426-461 mV) on the signal line which is pulled up through high resistance. When the HO2S-2 is cold, it produces no voltage and has extremely high internal resistance. The internal resistance of the sensor is much greater than the resistance of the bias pull-up resistor. However, when the sensor heats up, it produces voltage that overrides the bias voltage. This voltage is read by the PCM to determine the efficiency of the catalytic converter. Under normal conditions, low sensor voltage means high oxygen content/lean air-fuel mixture and vice versa. Normal sensor readings at steady cruise with a properly functioning catalytic converter will be around 500-800 mV. DTC P0140 sets when the HO2S-2 signal is inactive, not fluctuating out of the 426-461 mV range.
DTC Parameters
DTC P0140 will set if HO2S-2 is inactive -- voltage is not fluctuating outside the 426-461 mV range, when:
| • | The condition exists for longer than 2 minutes and 25 seconds. |
| • | The engine run time is greater than 1 minute. |
| • | No camshaft (cam), crankshaft position (CKP), engine coolant temperature (ECT), exhaust gas recirculation (EGR) evaporative emission, (EVAP) purge solenoid, fuel trim, intake air temperature (IAT), manifold absolute pressure (MAP), misfire or throttle position (TP) sensor DTCs have been set. |
DTC P0140 diagnostic runs continuously once the above conditions have been met.
DTC P0140 is a type B DTC.
Diagnostic Aids
Important: If DTC P0037 or P0038 is set, diagnose that DTC first. An HO2S-2 heater malfunction may slow the sensor activation time up long enough to set DTC P0140.
To locate an intermittent problem, use a scan tool to monitor HO2S-2 voltage with engine at normal operating temperature. Bias voltage (391-491 mV) will appear on the scan tool if there is an open anywhere in the sensor circuit.
