Fuel Tank Pressure Sensor: Description and Operation

Enhanced Evaporative Fuel Tank Pressure Sensor:

FUEL TANK PRESSURE SENSOR
The Fuel Tank Pressure sensor is a three wire strain gauge sensor much like that of the common MAP sensor. However, this sensor has very different electrical characteristics due to it's pressure differential design. The sensor measures the difference between the air pressure (or vacuum) in the fuel tank and the outside air pressure.
The sensor mounts at the top of the fuel tank sending unit. A three wire electrical harness connects it to the Control Module. The Control Module supplies a 5 volt reference voltage and ground to the sensor The sensor will return a voltage between 0.1 and 4.9 volts. When the air pressure in the fuel tank is equal to the outside air pressure, such as when the fuel fill cap is removed, the output voltage of the sensor will be 1.3 to 1.7 volts.
When the air pressure in the tank is 4.5'' H20 (1.25 kPa), the sensor output voltage should be 0.5 ± 0.2 volts. When there is neither vacuum or pressure in the tank, the sensor voltage should be at 1.5 volts at -14" H20 (-3.75 kPa) the sensor output voltage should be 4.5 volts ± 0.2 volts.