P0422
Main Catalyst Efficiency Below Threshold (Bank 1)
Generic main catalyst efficiency code on bank 1 — used by some manufacturers in addition to or instead of P0420. Indicates the same root cause — degraded oxygen storage in the main catalyst.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Common causes
Ordered by how often each turns out to be the cause.
- Catalyst aged or contaminatedCommon
- Oxygen sensor driftPossible
Parts involved
- Catalytic Converter
- Oxygen Sensor Upstream
- Oxygen Sensor Downstream
P0422 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.