P0430 Catalyst System Efficiency Below Threshold (Bank 2)
The same catalytic converter efficiency failure as P0420, measured on the engine's second cylinder bank.
Emissions
Only V-shaped and flat engines have a bank 2, and on those it usually has its own converter and its own pair of oxygen sensors. P0430 is the bank 2 version of P0420, and everything about diagnosing it is the same — including the fact that the converter is not automatically the guilty part.
Diagnose P0430 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you needCan I keep driving?
Driveable
Yes, normally with no noticeable change in how the car drives.
How serious
Low urgency mechanically, but it fails emissions testing.
Symptoms you'll notice
- Check-engine light with normal drivability
- Failed emissions test
- Sulphur smell from the exhaust
- Sometimes stored together with P0420
What causes P0430
Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.
Failing bank 2 downstream oxygen sensor
Check this before the converter — it is a fraction of the cost. Having a healthy bank 1 to compare against is a real advantage here: put both banks' sensor waveforms side by side on live data.
Exhaust leak on bank 2
A leak between the two sensors on that side draws in air and mimics a dead converter.
Worn-out bank 2 catalytic converter
The genuine cause once sensors and leaks are eliminated.
Upstream misfire or rich condition on that bank
P0175 or a bank 2 misfire code alongside P0430 identifies what is destroying the converter. Fix the cause or the replacement will follow the original.
Both P0420 and P0430 stored together
Two converters rarely wear out simultaneously. When both banks report low efficiency at once, suspect something shared — an engine-wide rich condition, oil consumption, or a fuel-system problem — rather than buying two converters.
How to diagnose it
- Note whether P0420 is stored too; both banks at once points at a shared upstream cause.
- Compare bank 1 and bank 2 downstream sensor waveforms directly — the healthy bank is your reference for what normal looks like on this engine.
- Inspect the bank 2 exhaust for leaks.
- Check for misfire and fuel-trim codes on that bank and fix them first.
Parts you might need
Tools for the job
- OBD-II scanner with live data
- Oxygen sensor socket
- Infrared thermometer
Related trouble codes
- P0420 — Catalyst System Efficiency Below Threshold (Bank 1)
- P0175 — System Too Rich (Bank 2)
- P0300 — Random/Multiple Cylinder Misfire Detected
Fitment matters. Causes and parts above are the common cases for P0430 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.