Circuit Description

The DTC P0120 Throttle Position (TP) sensor circuit diagnostic detects an out of range sensor signal. The TP sensor is a potentiometer whose resistance value changes along with throttle valve position. Powertrain Control Module (PCM) provides a 5-volt reference voltage to TP sensor. PCM reads voltage across TP sensor and uses voltage to calculate percentage of throttle valve opening. TP sensor resistance decreases as throttle valve opening increases. When TP sensor resistance decreases, voltage monitored by PCM increases. TP sensor resistance increases when throttle valve opening decreases, therefore, voltage monitored by PCM, will decrease. See TP SENSOR OPERATION  table.