Alero L4-144 2.4L DOHC VIN T SFI (2000)
Throttle Position Sensor: Description and Operation
The Throttle Position (TP) sensor (2) is a potentiometer connected to the throttle shaft on the throttle body. The TP sensor electrical circuit consists of a
5 volt supply line and a ground line, both provided by the Powertrain Control Module (PCM), and a signal line to the PCM. By monitoring the voltage
on this signal line, the PCM can calculate the throttle position angle as a percentage. As the throttle valve angle is changed as the accelerator pedal is
moved, the output of the TP sensor also changes. At a closed throttle position, the output of the TP sensor is approximately 0.6 volt. As the throttle valve
opens, the output increases so that, at wide open throttle, the output voltage should be near 5 volts.
The PCM can determine fuel delivery based upon the throttle valve angle. A broken or loose TP sensor can cause intermittent bursts of fuel from the
injectors and an unstable idle, because the PCM thinks the throttle is moving. A high or low voltage problem in the TP sensor circuits should set either a
DTC P0122 or DTC P0123. The PCM also has the capability of setting a DTC P0121 if the sensor is reading out of range. Once a diagnostic trouble
code is set, the PCM will use a default value for the TP sensor, and some vehicle performance will return.
See the TP Sensor Replacement portion of the service manual for the replacement of the TP sensor. The TP sensor is not adjustable.
