P2AA1: Alternative Fuel Return Line Valve Control Circuit High
What to do
The tell is a hot restart. If the car runs well cold and well on a journey, but stumbles for the first minute after a short stop, that is fuel boiling in the rail because it is not circulating. It will fall back to petrol. Worth describing exactly that way to whoever looks at it.
What this code means
The control circuit for the gaseous fuel return line valve is faulty.
A return line means fuel that reaches the engine bay and is not burned goes back to the tank, and on a gas system that serves a purpose petrol return lines do not.
Circulating fuel carries heat away. An engine bay is hot, and LPG held stationary in a rail beside a hot engine will boil — which on a liquid-injection system destroys the metering, because the injector is calibrated for liquid and vapour occupies far more volume for the same mass. Keeping fuel moving keeps it liquid.
So the return line is not a pressure-relief afterthought; it is part of how the system holds the fuel in the right phase. A restricted or closed return produces exactly the fault the circulation exists to prevent: fuel boiling in the rail after a hot restart, which is why the classic symptom is a car that runs perfectly cold, is fine on a long journey, and stumbles for the first minute after a ten-minute stop at a petrol station.
That hot-restart signature is the diagnostic, and it is easy to dismiss as a fuelling glitch because it clears itself once fresh fuel has circulated.
At or above the upper limit, usually an open coil or a short to supply.
Likely causes
Start here
- Faulty alternative fuel return line valve · specialist
- Corroded or loose connector · specialist
Less common
- Open circuit in control wiring · specialist
- Control module driver failure · specialist
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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