C Yukon 2WD V8-5.7L VIN R (1999)
Fuel Tank Pressure Sensor: Description and Operation
The Fuel Tank Pressure sensor is a 3 wire strain gauge sensor much like that of the MAP sensor, however this sensor has a very different electrical
characteristic due to its 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 varies a voltage between 0.1-4.9 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 measure 1.3-1.7 volts.
When the air pressure in the tank is 4.5 inches H2O (1.25 kPa), the sensor output voltage should measure 0.3-0.7 volts.
The sensor voltage will be approximately 1.5 volts when the fuel tank pressure is equalized with ambient pressure. The sensor voltage increases to
approximately 4.5 volts when a vacuum of 14 inches of H2O (-3.75 kPa) is detected.
