Fuel Rail Temperature Sensor
WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The Fuel Rail Temperature (FRT) sensor is a thermistor. The FRT thermistor has high resistance when cold and low resistance when hot. The Powertrain Control Module (PCM) supplies about 5 volts to the FRT sensor signal circuit. When the FRT sensor is cold its resistance is high and the signal voltage is high. As the FRT sensor warms and resistance drops, less signal voltage is monitored by the PCM. The FRT signal is used by the PCM for fuel trim adjustment.