P0422 code meaning
Catalyst 2 Efficiency Below Threshold Bank 1
Powertrain system Generic code P04xx codes Check engine light
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. 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.
P0422 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0422
- Check engine light on
- Emission test problems
- Diesel: possibly more frequent filter regenerations
Common causes of P0422
- Most likelyMain or underfloor catalyst aged or poisoned
- PossibleDiesel: exhaust fuel injector coked, doses too little
- PossibleTemperature or oxygen sensor after the catalyst wrong
- Less likelyMisfire or mixture fault as prior damage
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Underfloor catalystExhaust temperature sensorEngine control module
What each part of P0422 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 22 | The exact fault in that area. |
What to do next
- Note P0422 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0422
What does P0422 mean?
P0422 means "Catalyst 2 Efficiency Below Threshold Bank 1". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0422?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0422 fail an emissions test?
Yes, it can. P0422 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0422 to fix?
Difficulty: medium. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P0422 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.