P2423HC Adsorption Catalyst 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
- Some very low emission petrol engines add a hydrocarbon trap: an adsorbing layer holds back unburned fuel during a cold start and releases it once the main catalyst has lit off. P2423 means the bank 1 trap no longer retains enough. Nissan uses the code, named HC adsorption catalyst function, on the 2010-2012 Altima with the QR25DE in California SULEV form. Its bulletin NTB20-020 stretches warranty on the front exhaust pipe that carries the catalyst to 16 years/170,000 miles for 2010-2011 cars and 10 years/120,000 miles for 2012, tied to an ECM reprogramming campaign. Nissan does not publish the threshold. CARB places such traps under other emission controls with an approved monitoring plan. The car drives normally.
- What you may notice
- Check engine light, no noticeable driving change
- Higher cold-start hydrocarbon emissions
- Likely causes
- LikelyAdsorber layer aged or saturated with deposits
- PossibleECM calibration affected by a manufacturer campaign (Nissan Altima SULEV)
- RareDamage from misfires or oil consumption
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.