P0156 - OBD-II Trouble Code

Oxygen Sensor Circuit Malfunction (Bank 2, Sensor 2)

Our emissions expert has put together the following information about the P0156 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the 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