P2A25: Vanne de coupure B du réservoir de carburant alternatif — circuit de commande haut

The control circuit for one of the gaseous fuel tank shutoff valves is faulty.

"Alternative fuel" in the standard means a gaseous fuel — LPG, autogas or compressed natural gas — and a car running one is carrying a second, largely parallel fuel system.

Most such vehicles are bi-fuel: a full petrol system, and beside it a pressurised tank, its own lines, its own injectors, and a control module of its own. The car starts on petrol and switches to gas once it has warmed up — because the vaporizer that turns liquid gas into vapour is heated by engine coolant, a detail that turns out to matter for diagnosis — and either fuel can run it.

Which produces the diagnostic property that makes this whole range different: the car has a working fallback. A fault that would strand a petrol car merely makes this one switch back and keep going. So the complaint is almost never "it stopped" — it is "it will not run on gas any more", or "it keeps dropping back to petrol", and the driver may have tolerated it for months because the car still works and only the fuel bill changed.

The second consequence is that a gas system is a pressure system, and the parts in this range exist mostly to contain and measure that pressure rather than to meter fuel. That is why the shutoff valves get their own codes and why they are treated as safety devices rather than as plumbing.

A tank shutoff valve is a safety device, and reading it as a fuel valve underplays what it is for.

A gaseous fuel tank holds its contents under real pressure — around 8 bar for LPG at summer temperatures, and up to 200 bar for compressed natural gas. A petrol tank leaks a puddle; a gas tank leaks continuously and invisibly until something ignites it. So the tank is fitted with an electrically held valve at its outlet, and the wiring is arranged so that the valve closes whenever it loses power — engine off, ignition off, crash sensor triggered, or a fault anywhere in its circuit.

That fail-closed design is why a fault here stops the gas system rather than degrading it. There is no partial state and no limp mode: the valve is either held open or the tank is isolated. The car simply runs on petrol.

And it is why the fault is easy to live with and worth not living with. A valve circuit that is intermittently open is a valve that may not open — but it is also, on the other side of the same fault, a valve whose ability to close on demand is no longer proven. The half nobody notices is the half that matters.

Valves B through E mean multiple tanks. Commercial conversions frequently carry two or more — a toroidal tank in the spare wheel well plus a cylinder in the load space is a common pairing — and each gets its own valve and its own code. The letter tells you which tank, and only the installer's documentation maps a letter to a physical location, because these are almost always aftermarket installations rather than factory fitments.

At or above the upper limit, usually an open coil or a short to supply.