Throttle Position Sensor: Description and Operation

Throttle Position Sensor:

Throttle Position Sensor (TPS):

PURPOSE
The PCM senses changes in the Throttle Position (TP) sensor output which controls fuel delivery. By monitoring the output voltage from the TP, the PCM can modify fuel delivery based on throttle valve angle. For example; power enrichment occurs when the throttle angle approaches wide open throttle. Acceleration enrichment occurs when the throttle angle increases abruptly, similar to an accelerator pump on a carbureted vehicle.



OPERATION
The TP Sensor is a three wire sensor or potentiometer which has a five volt reference, a reference ground, and a output signal from the sensor to the PCM. The sensor output signal is a DC voltage that varies with throttle angle. As the throttle valve angle changes, the voltage output of the TP also changes. At a closed throttle position, the output of the TP is low. As the throttle plate opens, the output voltage increases so that, at wide-open throttle, the output voltage should be approximately 5 volts.


DIAGNOSTIC NOTES
The TP can either be misadjusted, open, or shorted. If the sensor is open, the PCM will sense that the throttle is closed, and performance will be reduced. This will normally set a trouble code P022. If the switch is shorted, the PCM will sense that the vehicle is at WOT, and a trouble code P021 will be set. Intermittent problems can also set code P070. Once a trouble code is set, the PCM will substitute a value for the TP, and some vehicle performance will return.