DTC P0181: Fuel Temperature Sensor & Intake Air Temperature Sensor Temperature Not Within Specification: Description
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The fuel temperature sensor is a thermistor. The Engine Control Module (ECM) supplies the fuel temperature sensor a reference voltage of 5 volts on the signal circuit and also provides a low reference circuit to the sensor. When the fuel temperature sensor signal voltage remains near the supplied voltage cold and decreases the signal voltage as the sensor warms. The control module monitors the fuel temperature sensor signal circuit in order to calculate the temperature of the fuel entering the engine.