P0430: Catalyst System Efficiency Below Threshold — Bank 2
What to do
Driveable, will fail an emissions test. The same three questions as P0420 apply — exhaust leaks, rear sensor response, and the Mode 06 value — and it is worth asking how the other bank measures, because the comparison is informative.
What this code means
The bank 2 converter is below its efficiency threshold — the direct counterpart of P0420 on the engine's second cylinder bank, and only found on V-configuration and flat engines with two exhaust banks.
Everything in P0420 applies here, and one extra piece of evidence becomes available: compare the two banks. Two converters of the same age on the same engine rarely fail independently at the same moment, so a fault on one bank while the other passes comfortably points at something local to that bank — its rear oxygen sensor, or a leak in that side of the exhaust. Both banks failing together points instead at a whole-engine cause such as oil consumption or a long-standing rich condition.
Likely causes
Start here
- Aged or lazy downstream oxygen sensor · easy
- Exhaust leak before the sensor · moderate
- Failed catalytic converter · specialist
Less common
- Converter poisoned by oil or coolant consumption · specialist
- Prolonged rich running damaging the converter · moderate
- Misfire dumping unburnt fuel into the converter · moderate
- Aftermarket converter below original specification · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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