P0156 - OBD-II Trouble Code

Our automotive experts have put together the following information about the P0156 diagnostic trouble code. We've provided the common symptoms that occur when this code is set along with the frequent repairs that address the issues related to the P0156 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

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