P0431 Warm-up catalyst efficiency below threshold (bank 2)
What P0431 means
On an engine with two cylinder banks, the engine control unit compares the oxygen sensors before and after the bank 2 warm-up catalytic converter. The readings show the catalyst is no longer storing enough oxygen to clean the exhaust properly.
P0431 is a generic SAE J2012 code: it means the same on every make. The exact cause still depends on the car, so read the freeze-frame data before replacing parts.
At a glance
- Severity
- Medium
- Typical repair cost
- 400–1800 €
- Workshop time
- 1–4 h
- Repair difficulty
- Hard
- DIY possible
- No
- Check engine light
- Yes
- Affects emissions test
- Yes
Parts and labour at an independent workshop in Europe. Main dealers charge more; the cause decides the bill, not the code.
Symptoms
- Check engine light on
- Usually no change in how the car drives
- Possible sulphur smell
- Failed emissions test at technical inspection
Common causes
- Worn or contaminated catalytic converter on bank 2
- Faulty bank 2 downstream oxygen sensor
- Exhaust leak near the bank 2 sensors
- Misfires or rich running on bank 2
- Oil consumption contaminating the catalyst
Can I keep driving with P0431?
You can keep driving, but have it checked within one to two weeks to avoid failing the technical inspection.
What to check first
- Check for misfire, fuel trim or oxygen sensor codes on bank 2 and fix those first
- Inspect the bank 2 exhaust for leaks
- Compare bank 2 front and rear oxygen sensor signals in live data
- Replace the downstream sensor if faulty, otherwise replace the bank 2 catalyst
Related codes
- P0430 Catalyst system efficiency below threshold (bank 2)
- P043E EVAP leak detection reference orifice low flow
- P043F EVAP leak detection reference orifice high flow
- P0440 Evaporative emission (EVAP) system malfunction
- P0441 EVAP system incorrect purge flow
- P0421 Warm-up catalyst efficiency below threshold (bank 1)
- P0420 Catalyst system efficiency below threshold (bank 1)
- P0442 EVAP system small leak detected
Data: TORKO fault-code catalogue, built on OBDex (CC0-1.0) and reviewed against workshop practice. Informational only — it does not replace a diagnosis by a mechanic.
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