P0430 Code: Catalyst System Efficiency Below Threshold (Bank 2)
The catalytic converter on bank 2 (the side of the engine opposite cylinder 1, on V6/V8 engines) is no longer cleaning exhaust gases as effectively as it should. It is the bank-2 twin of P0420.
What this means for driving
As with P0420, this is an emissions fault rather than a safety-critical one, and the engine usually runs normally. The vehicle risk is the same: a failing converter can worsen, and an underlying misfire or fuel-mixture problem can damage it further. Have it assessed promptly, and expect an emissions-test failure while the light is on.
When in doubt, have a mechanic assess it promptly. If any of the red-flag symptoms below are present, stop driving and arrange a tow rather than risking it.
Important: This page is general information only — not professional mechanical advice and not a diagnosis for your specific vehicle. Fault causes and severity vary by make, model, year, and condition. A qualified mechanic should confirm any diagnosis before you make driving decisions or authorize repairs.
Red-flag symptoms: stop and get help
- Check-engine light flashing
- Noticeable loss of power
- Strong rotten-egg smell with poor running
- Overheating or rattling from underneath the car
Symptoms of P0430
- Check-engine light on (often the only symptom)
- Reduced fuel economy
- Slight loss of performance
- Rotten-egg smell from the exhaust
- Failed emissions test
Most likely causes, ranked
- Failing catalytic converter on bank 2
- Faulty downstream oxygen sensor on bank 2
- Exhaust leak near the bank-2 converter
- Engine misfire or rich/lean condition affecting bank 2
- Oil or coolant contamination reaching the exhaust
How a mechanic diagnoses it
- Live oxygen-sensor data compared between banks — bank 2's downstream sensor mirroring its upstream sensor points to the converter.
- Exhaust inspected for leaks or converter damage.
- Engine checked for misfires or fuel-trim issues as a possible root cause.
Likely fixes
- Replace downstream oxygen sensor (bank 2)
- Repair exhaust leak
- Fix underlying misfire or fuel-trim problem
- Replace catalytic converter (bank 2) (Shop job)
Repair costs vary by vehicle, region and shop. Get a quote from a local mechanic.
Related codes
- P0420: Catalyst System Efficiency Below Threshold (Bank 1)
- P0300: Random/Multiple Cylinder Misfire Detected
- P0171: System Too Lean (Bank 1)
- P0174: System Too Lean (Bank 2)
CheckMyCarCode content is general information only and is not a substitute for professional diagnosis. Trouble-code meanings are standardized for generic (P0xxx) codes, but causes, severity, and repairs vary by vehicle. If your car shows a red-flag symptom, stop driving and get professional help.