P0156 - OBD-II Trouble Code

OBD II Fault Code

  • OBD II P0156

Fault Code Definition
The Rear Catalyst Monitoring Oxygen Sensor evaluates the Catalytic Converter's emissions-reducing capability. Code P0156 is set when the Rear Oxygen Sensor signal does not show enough activity to indicate fuel control and closed loop fuel management.


  • 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 some cases, the NOx emissions will be elevated

Common Problems That Trigger the P0156 Code

  • Defective Bank 2 Rear Oxygen Sensor 
  • Faulty Bank 2 Rear Oxygen Sensor wiring or connections

Common Misdiagnoses

  • Oxygen Sensor is replaced when the problem is faulty sensor wiring or connections
  • Rear Oxygen Sensor is replaced when the problem is an exhaust leak before the Rear Oxygen Sensor