Fault code P0422 – a step-by-step guide to diagnosing and fixing it

Error code P0422 is displayed and the check engine light is on - what does this mean?

With this DTC, the OBD system detects that the efficiency of the main catalytic converter under bank 1 is below the expected threshold value. Error code P0422 relates to the exhaust gas purification system and is monitored by the lambda probes before and after the catalytic converter. For various manufacturers, this code may also be referred to as "Catalytic converter efficiency below threshold bank 1".

What can cause this fault code?

• Deterioration or failure of the main catalytic converter
• Defective lambda sensors before or after the catalytic converter
• Damaged or corroded exhaust system
• Engine problems with incomplete combustion
• Defective fuel injection or ignition system
• Dirty or clogged air filter
• Incorrect fuel quality or contaminated fuel
• Leaks in the intake system
• Defective engine management software

What symptoms occur in parallel with fault code P0422?

• Check engine light: The MIL light in the dashboard is permanently activated
• Reduced engine power: Noticeable loss of power when accelerating
• Increased fuel consumption: Significantly higher consumption than usual
• Exhaust odor: Unusual odors from the exhaust
• Jerking when idling: Unsteady engine running at low engine speeds
• Starting problems: Difficulty starting the engine, especially in cold weather
• Misfiring: Sporadic misfiring under load

How can the problem with error code P0422 be rectified?

• The repair requires a systematic approach to identify the root cause.
• Replacement of the main catalytic converter bank 1 if the diagnosis confirms irreversible deterioration of the catalytic coating
• Replacing the lambda probes before and after the catalytic converter if they measure outside the specification values or react sluggishly
• Repairing exhaust leaks by welding or replacing damaged pipes and seals in the exhaust system
• Repairing engine problems such as defective spark plugs, ignition coils or fuel injectors that lead to incomplete combustion
• Cleaning or replacing the air filter and checking the entire intake system for leaks
• Updating the engine control unit software if manufacturer-specific technical bulletins are available
• Fuel system cleaning with professional additives to remove deposits in injectors and combustion chambers