P0431: Catalyst 1 Efficiency Below Threshold Bank 2
What to do
Driveable, will fail an emissions test. Establish that the converter is genuinely at fault, and find what damaged it, before replacing it.
What this code means
The close-coupled warm-up converter on bank 2 is underperforming — the counterpart of P0421 on the second bank. Diagnosed identically, with the same caution about establishing the cause before replacing the part, and the same value in comparing the two banks against each other.
Likely causes
Start here
- Failed catalytic converter · specialist
- Exhaust leak before the sensor · moderate
- Aged or lazy downstream oxygen sensor · easy
Less common
- Misfire dumping unburnt fuel into the converter · moderate
- Prolonged rich running damaging the converter · moderate
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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