P0140 - OBD-II Trouble Code

OBD II Fault Code

  • OBD II P0140

Fault Code Definition
The Catalyst Monitoring Oxygen Sensor evaluates the rear most Catalytic Converter's emissions-reducing capability. Code P0140 is set when there is no activity in the signal from the Rear Oxygen Sensor.


  • Check Engine Light will illuminate
  • In many cases, no abnormal symptoms may be noticed
  • In some cases, the vehicle will fail an Emissions Test
  • In many cases, the NOx emissions will be elevated

Common Problems That Trigger the P0140 Code

  • Defective Catalytic Converter
  • Faulty Rear Oxygen Sensor wiring or connections

Common Misdiagnoses

  • Oxygen Sensor is replaced when the problem is a defective Catalytic Converter
  • Oxygen Sensor is replaced when the problem is faulty sensor wiring or connections