P2A9D
Alternative Fuel High Pressure System Small Leak
The AFCM detects a small leak in the high-pressure alternative fuel system based on pressure decay rate after engine shutdown. Common in CNG vehicles where seal aging causes slow gas loss.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Common causes
Ordered by how often each turns out to be the cause.
- Seal aged at fitting or valveCommon
- High-pressure fitting loosePossible
Parts involved
- Alt Fuel High Pressure Lines
- Alt Fuel Seals
- Alt Fuel Tank
P2A9D 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.