Fault code P0431 – a step-by-step guide to diagnosing and fixing it

Error code P0431 is displayed and the check engine light is on - what does this mean?

The OBD system has detected that the efficiency of the catalytic converter in bank 2 is below the expected threshold value. This DTC P0431 specifically affects the catalytic converter of the second cylinder bank in V-engines or the downstream catalytic converter in in-line engines. This fault code may have slightly different names for different manufacturers such as BMW, Mercedes-Benz or Audi, but always refers to the catalytic converter efficiency.

What causes can this error code have?

• Defective or used catalytic converter in bank 2
• Faulty lambda sensor after the catalytic converter
• Damaged wiring of the oxygen sensors
• Leaking exhaust system upstream or downstream of the catalytic converter
• Defective lambda sensor upstream of the catalytic converter
• Dirty or clogged exhaust system
• Engine problems such as incomplete combustion
• Loose or corroded plug connections of the O2 sensors

What symptoms occur in parallel with fault code P0431?

• Increased fuel consumption: The vehicle requires more fuel than usual
• Loss of power: Noticeable reduction in engine power, especially when accelerating
• Exhaust odor: Unusual or increased exhaust odor inside the vehicle
• Check engine light: Continuous illumination of the check engine light
• Jerking when idling: Unsteady engine running at low engine speeds
• Failed emissions test: The vehicle does not pass the emissions test
• Black smoke: Dark exhaust fumes from the exhaust, especially when accelerating

How can the problem with error code P0431 be rectified?

• Repairing EOBD fault code P0431 requires a systematic approach to identify the root cause.
• Replace the catalytic converter: Replace the defective catalytic converter in bank 2 with a new or refurbished part after confirming the diagnosis
• Check and replace lambda sensors: Test both oxygen sensors (before and after the catalytic converter) with a multimeter and replace defective sensors
• Repair wiring: Check all O2 sensor wiring connections for damage, corrosion or loose contacts and repair accordingly
• Seal the exhaust system: Locate any leaks in the exhaust system using a smoke test and seal them with suitable repair agents or replacement parts
• Carry out engine maintenance: Perform a complete engine diagnosis, change spark plugs, air filter and perform an engine flush to correct combustion problems
• Clean connectors: Remove corrosion from all sensor plugs, treat with contact spray and ensure tight connections