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.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Common causes
Ordered by how often each turns out to be the cause.
- Catalyst aging / thermal damageCommon
- Oxygen sensor driftPossible
Parts involved
- Hc Adsorber Catalyst
- Oxygen Sensor
P2423 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.