P0430: Catalyst System Efficiency Below Threshold (Bank 2)
P0430 means Catalyst System Efficiency Below Threshold (Bank 2). The engine computer compares the upstream and downstream oxygen sensors to judge how well the catalytic converter on bank 2 (the side opposite cylinder 1) stores oxygen. This code means efficiency has dropped below the required threshold.
Can I keep driving? Safe to drive short-term, but have it checked to avoid failed emissions or worse fuel economy.
Common symptoms
- Check engine light on
- Usually no change in how the car drives
- Possible rotten egg (sulphur) smell
- Rattling from the converter if the substrate has broken up
- Failed emissions inspection
Possible causes
- Aged or damaged catalytic converter
- Exhaust leak near the oxygen sensors
- Faulty downstream (or upstream) oxygen sensor
- Engine problems that damaged the converter: misfires, oil burning or coolant leaks
- Aftermarket converter that does not meet the original specification
How to diagnose P0430
- Fix any misfire, fuel trim or oxygen sensor codes first; they often damage converters.
- Check for exhaust leaks ahead of the downstream sensor.
- Compare oxygen sensor signals at a steady 2,500 RPM: the upstream sensor should switch quickly while the downstream sensor stays relatively steady. A downstream sensor that mirrors the upstream one indicates low oxygen storage.
- Check the engine for oil consumption or coolant loss.
- Replace the converter only after the root cause has been fixed.
Do not replace the catalytic converter first. A converter fails for a reason, and a new one will fail again if misfires or oil burning are not fixed.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Related codes
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.