What does it mean?
On a gaseous fuel installation the pressure in tank A changes in ways the module can predict: it falls steadily as fuel is consumed, rises when the tank is refilled, and moves with tank temperature. This code is stored when the sensor signal is electrically valid but does not behave that way, for example staying fixed while fuel is used, not reacting to refuelling, or disagreeing with the other data the system holds about the tank. It is a plausibility fault rather than a wiring fault, so the sensor keeps reporting a number that simply cannot be true. The system will normally limit or refuse operation on the alternative fuel until the reading can be trusted again.
Symptoms
- Gas level gauge that is clearly wrong or does not move as fuel is used
- Premature changeover back to petrol even though the tank still holds fuel
- Refuelling not recognised, with the gauge staying where it was
- MIL (check engine lamp) on with a gas system warning
- Inconsistent range from one tankful to the next
- Uneven running or poor power while operating on the gaseous fuel
Likely causes
- Sensor element drifted with age so the reported pressure carries a constant error
- Sensor port blocked by debris, oily residue from the fuel, or ice in cold weather
- Sensor damaged internally by an overpressure event or by frost
- High resistance in the signal or ground circuit producing a steady offset
- Incorrect replacement sensor with a different pressure range or calibration
- Tank valve or filter restricted so pressure at the sensor does not follow the tank
- Faulty tank temperature input, which the module uses when judging the pressure value
How to fix it
- Compare the reported pressure with a mechanical gauge or with the expected value for the current tank temperature and fill level
- Watch the value live while the tank is refilled and while the vehicle is driven; a healthy sensor tracks both changes
- Check the tank temperature input, since the module uses it to judge whether the pressure is plausible
- Measure voltage drop on the signal and ground circuits and inspect the connector for water and corrosion
- Depressurise the system using the correct safety procedure, then remove the sensor and inspect its port for debris, oily residue or ice
- Check the tank valve and any filter for restriction that would isolate the sensor from real tank pressure
- Fit the correct specification sensor when the wiring and the tank side are proven, then verify the reading over a full fill and use cycle