What does it mean?
This code sets when the voltage on the alternative fuel tank temperature sensor circuit drops below the minimum the module accepts. In the usual thermistor arrangement the module supplies a reference through an internal pull-up resistor, and the sensor pulls the signal down as it gets hotter, so a very low voltage is interpreted as an implausibly high tank temperature. Because a CNG or LPG tank cannot physically reach such a temperature during normal driving, the module treats the reading as an electrical failure rather than a genuine measurement. The most common source is a short to ground in the signal wire or a sensor that has shorted internally. Once the code is set the fuel quantity calculation loses its temperature correction and the gas gauge becomes unreliable.
Symptoms
- MIL (check engine lamp) on with a gaseous fuel system fault stored
- Tank temperature displayed at the top of the scale on a scan tool regardless of conditions
- Gas fuel gauge inaccurate or reading incorrectly after a refill
- Changeover to gas refused or aborted on some systems
- Range estimate that does not match consumption
- No obvious engine running complaint on gasoline
Likely causes
- Signal wire shorted to ground along the underbody harness run
- Water or corrosion in the tank sensor connector bridging the signal pin to ground
- Thermistor shorted internally, giving near zero resistance
- Chafed insulation where the loom crosses the tank straps, subframe or a bracket
- Signal wire pinched during previous underbody or tank work
- Sensor of the wrong specification fitted, with a much lower resistance curve
- Control module input circuit failure, the least likely explanation
How to fix it
- Read the live tank temperature; a value pegged at maximum on a cold vehicle confirms an electrical fault rather than a hot tank
- Disconnect the sensor and see what the scan tool shows. If the reading swings to minimum temperature, the harness is intact and the sensor is shorted
- If the reading stays at maximum with the sensor unplugged, the signal wire is shorted to ground and must be traced
- Measure the sensor resistance and compare it against the specification for the ambient temperature
- Inspect the connector for water, salt and corrosion, and check the loom for rub-through along the underbody
- Repair the shorted conductor or damaged connector, protect and re-route the harness, then clear the code
- Replace the tank temperature sensor when its resistance is far below specification and the wiring measures good