DTC P0121: TP Sensor Performance: Description

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the throttle position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with a 5-volt reference circuit, a low reference circuit and a signal circuit.

The PCM provides the TP sensor with 5 volts on the 5-volt reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide-Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to more than 4 volts through the TP sensor signal circuit. When the conditions for running the DTC are met, the PCM will use the Manifold Absolute Pressure (MAP) sensor to determine if the predicted operating range of the TP sensor is correct. If the PCM detects that the TP sensor voltage is out of the predicted range DTC P0121 sets.