Grand Prix V6-191 3.1L VIN M SFI (1998)
Throttle Position Sensor: Description and Operation
DESCRIPTION
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 throttle position. As the throttle valve angle is changed (accelerator pedal 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 output increases so that at Wide Open Throttle (WOT), the output
voltage should be above 4 volts.
OPERATION
The PCM calculates fuel delivery based on 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 volts reference or signal circuits
should set either a DTC P0122 P0123, P1350. A hard failure with the TP sensor ground circuit may set DTCs P0107, P0112, P0123 or P0117. Once a
DTC is set, the PCM will use an artificial default value based on engine RPM and mass air flow for throttle position and some vehicle performance
will return. 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 will set if an intermittent high or low circuit failure is being detected.
The PCM can also detect a shifted TP sensor. The PCM monitors throttle position and compares the actual TP sensor reading to a predicted TP value
calculated from engine speed. If the PCM detects an out of range condition, DTC P0121 will be set.
