Throttle Position Sensor: Description and Operation

Throttle Position Sensor:

The Throttle Position Sensor (TPS) 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 ECM. The sensor output signal is a DC voltage that varies with throttle angle. As the throttle valve angle changes, the voltage output of the TPS also changes. At a closed throttle position, the output of the TPS is low. As the throttle plate opens, the output voltage increases so that, at wide-open throttle, the output voltage should be approximately 5.0 volts.

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

The TPS can either be misadjusted, open, or shorted. If the sensor is open, the ECM will sense that the throttle is closed, and performance will be reduced. This will normally set a trouble code E022. If the switch is shorted, the ECM will sense that the vehicle is at WOT, and a trouble code E021 will be set. Once a trouble code is set, the ECM will substitute a value for the TPS, and some vehicle performance will return.