DTC P0121: TP Sensor Angle Out Of Range: Description
WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. 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 about 5 volts on the TP sensor reference voltage circuit. The PCM also supplies a ground circuit to the TP sensor. When the throttle is depressed the TP signal voltage rises to near the supplied 5 volts. As the throttle is released the TP signal voltage drops to around 0.6 volt. The PCM and the Alternative Fuels Engine Control Module (AF ECM) monitor the TP signal circuit voltage and determine the angle or opening of the throttle blade.
This DTC is used to indicate a throttle angle that is greater than calculated, based upon engine speed and engine MAP.