P2A4A: Alternative Fuel Tank C Pressure Sensor Circuit Intermittent/Erratic
What to do
The car may switch between gas and petrol unpredictably. The sensor connector is at the tank, usually under the boot floor — a common cause is simply that it has been knocked or has corroded, which is a cheap fix if that is all it is.
What this code means
The pressure sensor circuit on gaseous fuel tank C is intermittent.
Tank pressure on a gas system is not a fuel-level reading, and confusing the two is the mistake this family invites.
LPG in a tank is a liquid with vapour above it, and the pressure of that vapour is set almost entirely by temperature rather than by how much is left. A tank that is nearly empty and one that is nearly full read close to the same pressure at the same temperature — and the same tank reads perhaps 4 bar on a winter morning and 10 bar after a summer afternoon parked in the sun.
So the module needs this reading for two quite different jobs. It is how the system knows what pressure the gas will arrive at, which changes how long the injectors must be held open for a given quantity of fuel. And it is how the system detects a leak — a tank whose pressure falls when the temperature has not is losing its contents.
Level is measured separately (P2A5F), which is why both exist.
A pressure sensor that reads wrong therefore mis-fuels the engine rather than mis-reporting the gauge. Reading high, the module under-delivers and the engine runs lean, which on gas means high combustion temperatures and, over time, damaged valve seats. That is the expensive failure mode of a cheap sensor, and it is why a lean-running gas conversion is worth taking seriously rather than tuning around.
Note this variant is numbered apart from its own family — the four circuit codes run contiguously and the intermittent one sits after them, which is a pattern repeated for every sensor family in this stretch. Do not infer it from the block.
On a tank sensor, intermittent is nearly always the connector. It lives at the tank, which on a conversion means under the boot floor or in the spare wheel well — reachable by road spray, and frequently disturbed by anyone loading luggage. Found by moving the harness with the reading live, not by measuring at rest.
Likely causes
Start here
- Corroded or loose connector · specialist
- Intermittent wiring fault · specialist
- Faulty fuel tank pressure sensor · specialist
Less common
- Water ingress into connector · 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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