P2A9A: Alternative Fuel Tank Select Valve C Control Circuit Performance
What to do
Watch your range and how much gas the car actually takes at a refill. If range has roughly halved and the tank takes far less than it used to, fuel is being stranded in a tank the system cannot reach — that is this fault, and nothing is leaking.
What this code means
The control circuit for gaseous fuel tank select valve C is faulty.
A tank select valve is what makes multiple gas tanks behave as one fuel supply, and its failures are quiet by nature.
Conversions often carry more than one tank — a toroidal tank in the spare wheel well plus a cylinder in the load space is a common pairing — because a single tank of usable size gives poor range compared with petrol. The select valve chooses which one is feeding the engine, and the module switches between them as they empty.
Which is why a stuck select valve does not stop the car. It strands fuel. The system draws one tank down, cannot switch, and reports itself out of gas with half its capacity still full — so the complaint is a range that has suddenly halved, and the gauge is telling the truth about the tank it can see.
That is a diagnosis nobody reaches from the symptom, because "my range halved" sounds like a leak or a consumption problem. The tell is that the total refill quantity at the pump has halved too, which an owner can check without any equipment.
Note the letter is the valve, not the tank, and on an aftermarket installation only the installer's documentation maps either to a physical location.
Likely causes
Start here
- Faulty alternative fuel tank select 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
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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