Diagnostic Trouble Code (DTC) P0140 Rear Heated Oxygen Sensor No Activity

Diagnostic Trouble Code (DTC) P0140

Rear Heated Oxygen Sensor No Activity




            Features of the Circuit


  • A voltage approximately of 450mm volts is generated by the ECM between the ECM terminals 64 and 13.
  • If the Exhaust Is RICH:    The Heated oxygen (O2) sensor is devised to alter the voltage                                                   between a range of about 1volt.
  • If the Exhaust Is POOR:  The Heated oxygen (O2) sensor is devised to alter the                                               voltage between a range of about 100mm volt.
  • The Heated O2 sensor acts quite like an open circuit and does not generate any voltage when it is below 360°C(600°F).
  • An "open loop" operation is created by an open O2 sensor circuit or a cold O2 sensor    



Time for setting the DTC

Task boosted after DTC sets

When will DTC clear?

1) Engine running time is > 30 seconds. When there is a closed loop condition prevailing in the engine controls system


1) The Malfunction Indicator Lamp (MIL) will be seen glowing.


1) The MIL will go off after three repetitive ignition cycles in which the diagnostic runs perfectly

2) If the Engine Coolant Temperature is > 70°C (158°F).


2) The ECM will begin to record operating conditions at the time when the diagnostic fails which will be stored in the Freeze Frame.


2) A history DTC will clear by itself after 40 successive warm-up cycles flawlessly

3) If the engine speed ranges within 1,300rpm and 3,000rpm.


3) The vehicle will operate when there is an Open Loop condition existing.



3) The scan tool can be used to remove all existing DTCs.


4) When the vehicle has a speed around 26km/h (16.2mph) to 54km/h(33.6mph

4) A history Diagnostic Trouble Code (DTC) will be stored.


4)  Disconnecting the ECM battery feed for 10 seconds.


5) If the manifold air pressure is > 700hPa

5) The Coolant Fan will be seen turning ON.



6) If the exhaust has no transition from rich side to lean side or vice versa during 7.8 seconds even with a forcing of O2 sensor controller.




7)  When DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0137, P0138, P1671, P0300, P0335, P0336, P0341, P0400, P0404, P0405, P0644, P0645 are NOT SET.





                          Diagnostic Tools Available


  • If a Closed Loop situation prevails then normal scan tool voltage fluctuates between 0.15 to 8.5mV.
  • If you find that DTC P0140 is intermittent, then refer to "Intermittent" in this section.