P0431
Catalyst 1 Efficiency Below Threshold Bank 2
Catalyst / emissions
Generic OBD-II
Medium
What it means
P0431 means the catalytic converter on bank 2 isn't cleaning the exhaust as efficiently as the ECM expects, based on the upstream and downstream oxygen sensor readings. The engine still runs normally. The usual cause is an aged converter, but a faulty downstream O2 sensor or an upstream misfire can also trigger it.
Medium
Can I keep driving? Safe to keep driving — the engine runs normally; this is an emissions-efficiency fault, so fix it to pass inspection and stop the light.
Common symptoms
What you'll notice
- Check-engine light on (often the only sign)
- May fail an emissions/smog test
- Occasionally a faint sulfur or rotten-egg smell from the exhaust
- Slightly worse fuel economy in some cases
Common causes
Most likely first
- Aged or failed catalytic converter on bank 2 (most common)Likely
- Faulty bank 2 downstream oxygen sensor giving a false efficiency readCommon
- Exhaust leak near the converter or the rear O2 sensorCommon
- An upstream misfire or rich condition that has damaged the converterLess often
How to diagnose & fix
Work through it in order
- Confirm there are no misfire, fuel-trim, or O2-sensor codes first — fix those before condemning the converter.
- Compare the bank 2 upstream and downstream O2 sensor traces live; a downstream sensor mirroring the upstream points to a worn converter.
- Inspect the exhaust for leaks near the converter and rear sensor.
- Replace the bank 2 downstream O2 sensor if it's proven faulty; otherwise replace the bank 2 catalytic converter.
- Clear the code and let the catalyst monitor re-run to confirm the repair.
FAQ
Quick answers
Is it safe to drive with P0431?+
Yes. The car drives normally; this code means the bank 2 converter isn't cleaning the exhaust well enough, so fix it to pass emissions.
Can I just clear P0431?+
It returns after the catalyst monitor re-runs unless the converter or the underlying cause is repaired.
Related codes
Often seen with P0431
Read & clear P0431 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX