P2423 code meaning
HC Adsorption Catalyst Efficiency Below Threshold (Bank 1)
Powertrain system Generic code P24xx codes Check engine light
What P2423 means
Some very low emission gasoline 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.
P2423 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P2423
- Check engine light, no noticeable driving change
- Higher cold-start hydrocarbon emissions
Common causes of P2423
- Most likelyAdsorber layer aged or saturated with deposits
- PossibleECM calibration affected by a manufacturer campaign (Nissan Altima SULEV)
- Less likelyDamage from misfires or oil consumption
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hc adsorber catalyst
What each part of P2423 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 23 | The exact fault in that area. |
What to do next
- Note P2423 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 P2423
What does P2423 mean?
P2423 means "HC Adsorption Catalyst Efficiency Below Threshold (Bank 1)". Some very low emission gasoline 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P2423?
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 P2423 fail an emissions test?
Yes, it can. P2423 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 P2423 to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P2423 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.