Trooper LS V6-3.5L (1998)
Throttle Position Sensor: Description and Operation
General Description
The throttle position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. The PCM monitors the voltage on the signal
line and 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.
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-volt reference or signal circuits will
set either a DTC P0122 or DTC P0123. A hard failure with the TP sensor ground circuit may set DTC P0123 and DTC P0112. Once a DTC is set, the
PCM will use an artificial default value based on engine RPM and mass air flow for the 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.
