Throttle Position Sensor: Description and Operation

The throttle position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the PCM calculates the throttle position. When the throttle valve angle is changed as the accelerator pedal is moved, the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens the TP sensor voltage increases so that, at wide open throttle (WOT), the TP sensor voltage should be above 4 volts. The PCM calculates the fuel delivery based upon the throttle valve angle (driver demand).

A broken or loose TP sensor may cause intermittent bursts of fuel from an injector and unstable idle because the PCM thinks the throttle is moving. A hard failure in the TP sensor 5 volt reference or signal circuits should set either a DTC P0122 or DTC P0123. A hard failure in the TP sensor ground circuit may set DTCs P0123 and P0117. Once a DTC is set, the PCM uses an artificial default value based upon engine RPM and mass air flow for the throttle position and some vehicle performance returns. A high idle may result when either DTC P0122 or DTC P0123 is set.

The PCM can detect intermittent TP sensor faults. DTC P1121 or DTC P1122 is set if an intermittent high or low circuit failure is detected. The PCM can also detect a shifted TP sensor. The PCM monitors the throttle position and compares the actual TP sensor reading to a predicted TP value calculated from the engine speed. If the PCM detects an out of range condition, DTC P0121 is set.