What it means
The AFCM detects pressure decay in the alternative fuel rail consistent with injector leakage. Even with all injectors commanded closed, fuel flows back into the rail.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The AFCM monitors pressure in the alternative-fuel rail after the injectors are commanded closed. It sets P2A40 when pressure decays in a pattern consistent with fuel leaking through an injector or its seal. A leaking injector can disturb starting and idle, and an external leak can create a fuel odor.
Common causes
Most likely first.
- Injector seat worn - leaks closed
- Injector seal aged - external leak path
Symptoms
- Check-engine light
- Rough idle
- Hard starting
- Fuel odor
How to diagnose it
- If you smell alternative fuel, see a leak, or feel unwell, move away from the vehicle and do not start it; have the system made safe before testing.
- Use a scan tool to save freeze-frame data and check rail-pressure behavior after the AFCM commands the injectors closed.
- With the system depressurized according to the manufacturer’s procedure, inspect injector bodies, seals, and rail connections for leakage or damage.
- Have rail-pressure decay and injector sealing tested using the manufacturer’s specified procedure.
- If no external leak is found, isolate and test injectors to identify a worn seat or seal that leaks when closed.
Common fixes
- Replace an injector with a leaking seat if the sealing test confirms it.
- Replace an aged or damaged injector seal causing an external leak path.
- Repair a leaking rail connection or damaged sealing surface identified during inspection.
Can I keep driving?
Do not drive if you smell fuel, see a leak, or the engine is hard to start or running roughly; fuel leakage can create a fire risk and worsen running problems. Arrange prompt diagnosis, and keep ignition sources away from any suspected leak.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.