Powertrain, generic · Auxiliary emission controls
P0422 Catalyst 2 Efficiency Below Threshold Bank 1
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
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.
Likely causes
Main or underfloor catalyst aged or poisoned
Diesel: exhaust fuel injector coked, doses too little
Temperature or oxygen sensor after the catalyst wrong
Misfire or mixture fault as prior damage
Symptoms
- Check engine light on
- Emission test problems
- Diesel: possibly more frequent filter regenerations
Repair estimate
DifficultyMediumWorkshop job
Parts and labour€400–2,500
Time1–3 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
underfloor catalystexhaust temperature sensorengine control module
Related codes
References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.