What does it mean?
This fault is the mirror image of a low circuit complaint on the same tank temperature sensor. With the module pulling the signal line up through an internal resistor, an open circuit or a very high sensor resistance leaves the input sitting close to reference voltage, which the module reads as an impossibly cold tank.
The strategy compares that value with ambient and intake air temperature and against the limits of the thermistor curve, and once the signal exceeds the upper voltage threshold for a calibrated time the code is stored. Because a broken connection produces exactly this signature, an open sensor, a corroded terminal or a cut wire are far more likely than an actual sub-zero tank. Fuel quantity calculation loses its density correction, so the gas gauge and range display stop being trustworthy.
Symptoms
- MIL (check engine lamp) on with a stored gaseous fuel fault
- Tank temperature shown at the bottom of the scale on a scan tool, even in warm weather
- Gas gauge reading incorrectly or failing to update after refuelling
- Delayed or refused changeover to gas because the module thinks the tank is extremely cold
- Inconsistent range prediction
- Otherwise normal engine operation on gasoline
Likely causes
- Open circuit in the signal wire or the sensor ground under the vehicle
- Corroded, pushed-out or broken terminal in the tank sensor connector
- Thermistor failed open internally
- Connector not fully latched after previous tank or underbody work
- Signal wire shorted to a reference or battery voltage from an adjacent circuit
- Rodent damage or crash damage to the underbody harness
- Control module input circuit failure, the least likely cause
How to fix it
- Read live tank temperature and confirm it disagrees sharply with ambient and intake air temperature
- With the ignition on, unplug the sensor and jumper the signal pin to ground at the harness connector. A reading that swings to maximum temperature proves the wiring and module are good
- If the reading stays at minimum with the pin grounded, trace the signal wire and the ground path for an open circuit
- Inspect the connector for spread terminals, corrosion, water damage and a broken locking tab
- Measure the sensor resistance; an infinite reading confirms an open thermistor
- Repair the open wire or terminal, protect the repair against water, then clear the code and verify the reading follows ambient temperature
- Replace the tank temperature sensor when the harness measures good and the element reads open