Powertrain, generic · Auxiliary emission controls
P0431 Catalyst 1 Efficiency Below Threshold Bank 2
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
Catalyst 1 is the first catalyst in the flow direction of bank 2 (the side without cylinder 1) – the close-coupled or warm-up catalyst that lights off first after a cold start; the older wording was Warm Up Catalyst. P0431 means it no longer converts enough. Mitsubishi V6 engines with manifold catalysts and GM's 3.0/3.2-litre V6 of 2004/05 with Bosch control report it: the rear sensor amplitude is compared with a model, and a quality factor above 0.625 (2004) or 0.375 (2005) sets the code after two trips. A Mitsubishi bulletin names coating coming off the manifold catalysts.
Likely causes
Close-coupled catalyst aged, overheated or coating detached
Misfire or rich running as prior damage
Sensor after the close-coupled catalyst sluggish or faulty
Engine module software (Mitsubishi: update for 2006 Eclipse V6)
Symptoms
- Check engine light on, otherwise often no change in driving
- Emission test failed (higher HC, CO, NOx)
- Rattling or loss of power if the catalyst has broken up
Repair estimate
DifficultyMediumDIY possible
Parts and labour€250–2,000
Time1–3.5 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
close coupled catalystdownstream oxygen sensorengine control module
Related codes
References: static.nhtsa.gov, gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.