OBD-II code · Powertrain (generic, extended)
P2423 HC Adsorption Catalyst Efficiency Below Threshold Bank 1
The ECU determines that the hydrocarbon adsorption catalyst on bank 1 no longer holds enough HC during cold start to meet emission targets. Often due to ageing or thermal damage.
Is it safe to drive with P2423?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyCatalyst aging / thermal damage
- PossibleOxygen sensor drift
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 2–6 h
- Emissions test
- Likely to fail
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Hc Adsorber Catalyst, Oxygen Sensor
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.