What P0422 means
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.
How the engine computer detects it
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. Gasoline engines with several catalysts usually report P0420 instead.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Emission test problems
- Diesel: possibly more frequent filter regenerations
Common causes
- Main or underfloor catalyst aged or poisoned Most likely
- Diesel: exhaust fuel injector coked, doses too little Possible
- Temperature or oxygen sensor after the catalyst wrong Possible
- Misfire or mixture fault as prior damage Less likely
How to diagnose P0422
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: underfloor catalyst, exhaust temperature sensor, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- 22
- Specific fault
Questions drivers ask
Can I drive with code P0422?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0422?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0422 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.