What does it mean?
The alternative fuel tank A level sensor measures how much liquid or gaseous fuel is physically present in the tank, and it is a different device from the tank pressure sensor. On LPG installations it is typically a float arm driving a resistive track or a magnetically coupled sender on the outside of the tank; on some systems it is a Hall effect or capacitive device. The module uses it to drive the gas fuel gauge, to warn the driver before the tank empties and to plan the changeover back to gasoline. This general circuit code is stored when the module cannot obtain a usable signal from that sender at all, whether the signal is out of range, missing or electrically implausible. The engine will normally still run on gas, but the driver loses any reliable indication of how much gas remains.
Symptoms
- Gas fuel gauge dead, stuck at one point or reading empty with a full tank
- MIL (check engine lamp) on with a gaseous fuel fault stored
- Low fuel warning appearing at the wrong time or not at all
- Unexpected changeover to gasoline because the module cannot confirm remaining gas
- Range display unavailable or clearly wrong
- Engine otherwise running normally on both fuels
Likely causes
- Corroded or water-damaged connector at the level sender, which sits on the tank under the vehicle
- Open or shorted wiring between the sender and the gaseous fuel control module
- Worn resistive track or a seized float arm inside the tank sender
- Failed magnetic coupling or displaced external sender on LPG multivalve assemblies
- Chafed harness where it passes tank brackets or the underbody
- High resistance sender ground or a corroded ground stud
- Gauge driver or module input failure, the least likely cause
How to fix it
- Read the live fuel level value and compare it with a known tank state, for example immediately after filling
- Unplug the sender connector and inspect for water, corrosion, bent pins and a damaged seal
- Measure the sender resistance or output at the connector and compare it with the specification for the current level, moving the float where the design allows
- Check for reference voltage and a good ground at the harness side with the ignition on
- Test the signal wire for continuity, short to ground and short to voltage back to the module
- Repair the damaged wiring or connector and reseal it against water intrusion, then clear the code and verify the gauge tracks correctly
- Replace the level sender or, on LPG multivalve systems, the sender assembly, once the wiring has been proven good