P0422
Catalyst 2 Efficiency Below Threshold Bank 1
Catalyst / emissions
Generic OBD-II
Medium
What it means
P0422 means the catalytic converter on bank 1 isn't cleaning the exhaust as well as it should — the computer compares the upstream and downstream oxygen sensors and sees efficiency below the limit. The car usually drives normally, but it's emitting more pollutants than allowed. Before replacing an expensive converter, rule out O2-sensor faults, exhaust leaks, and any misfire or fuel issue that could have damaged it.
Medium
Can I keep driving? You can keep driving. The car runs normally, but it's polluting more than allowed and will fail an emissions test until the cause is fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Failed emissions test
- Slightly reduced fuel economy
- Occasionally a faint sulfur (rotten-egg) smell from the exhaust
Common causes
Most likely first
- Aged or failing catalytic converter (bank 1)Likely
- Faulty or lazy downstream oxygen sensor giving a misleading readingCommon
- Exhaust leak near the sensors skewing the readingsCommon
- Upstream problem — misfire or rich/lean running — that damaged the converterLess often
- Failed ECM (rare — verify everything else first)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for any misfire, fuel-trim, or O2-sensor codes first — fix those before condemning the converter.
- Compare the upstream and downstream O2 sensor waveforms; a downstream sensor that mirrors the upstream one points to a worn converter.
- Inspect the exhaust for leaks between and around the sensors.
- Confirm the engine isn't running rich or misfiring and that fuel trims are normal.
- If the converter is genuinely worn out, replace it, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0422?+
Yes, the car drives normally. But it's exceeding emissions limits and won't pass inspection, and an underlying misfire or rich condition can worsen over time, so address it.
Can I just clear P0422?+
It will return after a drive cycle or two unless the converter or the condition that hurt it is repaired.
Related codes
Often seen with P0422
Read & clear P0422 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