Circuit Description
WARNING: This page is about a different car, the 1996 Pontiac Firefly and 1996 Geo Metro. However, it is still accessible from the selected car via links, so may be relevant.
Throttle Position (TP) sensor is a potentiometer whose resistance changes along with throttle valve position. PCM provides a 5-volt reference voltage to TP sensor. PCM reads voltage across sensor and converts it into a reference for throttle position. When TP sensor resistance decreases, throttle valve opening is increasing to WOT and voltage being monitored at PCM increases. When TP sensor resistance increases, throttle valve opening is decreasing to idle and voltage being monitored at PCM decreases. DTC P0121 will set when difference between expected TP sensor and actual input is greater than 11° for at least 3 seconds.