DTC P0121: TP Sensor Performance: Description

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 the following circuits:

• A 5-volt reference circuit.
• A low reference circuit.
• A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low 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 this DTC are met, the PCM will use the MAP sensor in order to determine if the predicted operating range of the TP sensor is correct. A skewed Manifold Absolute Pressure (MAP) sensor may cause this DTC to set. The MAP sensor should be tested for proper operation if the TP sensor is operating properly and this DTC continues to set.