Century V6-3100 3.1L VIN M SFI (1998)
Throttle Position Sensor: Testing and Inspection
Following is a short description of how the Throttle Position (TP) sensor can be diagnosed by using a scan tool. The scan tool can also be used to
compare the values for a normal running engine with the engine you are diagnosing.
DESCRIPTION
The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body.
OPERATION
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. The PCM calculates fuel delivery based on throttle valve angle (driver
demand).
DIAGNOSIS
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. Refer to System Diagnosis / Diagnostic Tables /
Diagnostic Trouble Code Tables. See: Computers and Control Systems/Testing and Inspection
