Fuel Tank Pressure (FTP) Sensor
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The Fuel Tank Pressure (FTP) Sensor, measures the difference between the fuel tank and outside air pressure. The PCM provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the PCM that can vary between 0.1 and 4.9 volts. As the fuel tank pressure increases, the FTP sensor voltage decreases, as the fuel tank pressure decreases the FTP sensor voltage increases. High pressure = high voltage. Low pressure vacuum = low voltage.