A traditional throttle-position sensor, pedal sensor or flap-position sensor can use a potentiometer. A resistive track is supplied with reference voltage and ground, and a moving wiper returns a voltage that changes with position. The basic concept is simple, but modern systems often use two independent tracks for safety.
Redundant tracks rarely produce identical voltages. Instead they are designed with a known relationship: one may rise while the other falls, or both may rise at different rates. The ECU checks whether that relationship remains plausible. This is why an electronic throttle code may refer to correlation rather than to one sensor simply being open or shorted.
A worn track can create a dropout in only one part of travel. A static voltage test at closed and wide-open positions may look normal while the signal briefly disappears in the middle. Slowly sweeping the sensor while watching graphing scan data, a min/max multimeter function or an oscilloscope can reveal the dropout.
Never force an electronic throttle plate unless service information says it is safe. Some throttle bodies contain reduction gears and motor mechanisms that can be damaged. Treat position sensors as part of a control system rather than as isolated variable resistors.