P0422Catalyst 2 Efficiency Below Threshold Bank 1
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Catalyst 2 is the second catalyst in the flow direction of bank 1 (the side with cylinder 1) – the main or underfloor catalyst behind the close-coupled one; the older wording was Main Catalyst. P0422 means it no longer converts enough. Only GM's small diesels are documented with this code: they assess the underfloor oxidation catalyst separately from the close-coupled one (P0421) by heat balance during filter regeneration, with an exhaust fuel injector ahead of it. Petrol engines with several catalysts usually report P0420 instead.
- What you may notice
- Check engine light on
- Emission test problems
- Diesel: possibly more frequent filter regenerations
- Likely causes
- LikelyMain or underfloor catalyst aged or poisoned
- PossibleDiesel: exhaust fuel injector coked, doses too little
- PossibleTemperature or oxygen sensor after the catalyst wrong
- RareMisfire or mixture fault as prior damage
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €400 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.