Throttle Position Sensor: Description and Operation

Throttle Position (TP) Sensor:

DESCRIPTION
The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body and is one of the most important sensors for engine and transmission control. The TP sensor has one end connected to 5 volts from the Powertrain Control Module (PCM) and the other to PCM ground. A third wire is connected to the PCM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes.

TP SENSOR VOLTAGE OUTPUT RANGE
At a closed throttle position, the voltage output of the TP sensor is low (approximately 0.5 volt). As the throttle valve opens, the output increases so that at wide-open throttle, the output voltage should be about 4.6 volts.

FUEL DELIVERY CALCULATION
By monitoring the output voltage from the TP sensor, the PCM can determine fuel delivery based on throttle valve angle (driver demand).

PCM AUTO-ZERO ABILITY
The PCM has the ability to auto-zero the TP sensor voltage if it is between about 0.3 - 0.9 volt. This means that any voltage in this window will be determined by the PCM to be 0% throttle. A failure in the TP sensor circuit should set a Diagnostic Trouble Code (DTC) 21 or 22.

DEFAULT VALUE
Once a DTC is set, the PCM will use a default value for TP sensor, and some vehicle performance will return.