Fuel Tank Temperature Sensor (CNG): Description and Operation

FUEL TANK TEMPERATURE (FTT) SENSOR

The FTT sensor is a thermistor mounted inside the HPL and is not serviceable separately from the HPL. The FTT thermistor has high resistance when cold and low resistance when hot. The FICM supplies about 5 volts to the FTT sensor signal circuit. When the FTT sensor is cold its resistance is high and the signal voltage is high. As the FTT sensor warms and resistance drops, less signal voltage is monitored by the FICM. The FTT sensor voltage is sent to the PCM through a PWM circuit. The volume of CNG will vary with temperature and pressure. Accurate CNG fuel level cannot be determined by pressure only. In order to compensate for the different volume factors the fuel tank temperature (FTT) sensor is mounted within the HPL. The PCM performs a calculation on the fuel tank pressure vs. the in-tank temperature. The PCM will then display the temperature corrected fuel level.