P0423 - OBD-II Trouble Code

Auto Systems and Repair

Main Catalyst Efficiency Below Threshold (Bank 2)

Our emissions expert has put together the following information about the P0432 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 P0432

Fault Code Definition
Code P0432 indicates that the Bank 2 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.


  • Check Engine Light will illuminate
  • In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0432 Code

  • Defective Catalytic Converter
  • Engine misfires have damaged the Catalytic Converter
  • Internal engine damage resulting in high oil consumption and/or a leaking Head Gasket has damaged the Catalytic Converter

Common Misdiagnoses

  • Oxygen Sensor(s) are replaced when the real problem is a damaged Catalyst
  • Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
  • Catalyst is replaced when a misfiring engine is the real problem
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