Fuel Rail Pressure Sensor
WARNING: This page is about a different car, the 2004 Ford Pickup Heritage. However, it is still accessible from the selected car via links, so may be relevant.
The fuel rail pressure (FRP) sensor is a pressure transducer that converts pressure to voltage through a piezo-resistive element. The FRP sensor is used to adjust the injector combination according to supply pressure and allows the vehicle to start in ALT fuel mode at a minimum of 517 kPa (75 psia). The resistance of the sensor increases as the pressure increases and decreases as the pressure decreases.