DTC P0121: TP Sensor Performance: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
The Throttle Position (TP) sensor is a potentiometer. The Powertrain Control Module (PCM) supplies the TP sensor:
- A 5-volt reference circuit.
- A low reference circuit.
- A signal circuit.
When the throttle is depressed, the TP sensor signal rises to near the reference voltage. When the throttle is released, the TP sensor signal decreases from the reference voltage. The control module monitors the TP sensor signal circuit voltage in order to determine the throttle blade angle, or opening. This Diagnostic Trouble Code (DTC) determines if the Throttle Position (TP) sensor signal input to the Powertrain Control Module (PCM) does not closely match what the predicted value for the TP sensor should be. The PCM calculates what the TP signal voltage should be based on engine RPM. If the TP sensor voltage and the predicted TP sensor values do not closely match, this DTC will be set.