Throttle Position Sensor: Description and Operation

Throttle Position Sensor:

PURPOSE
The Throttle Position Sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. The TPS supplies a signal indicating the position of the throttle shaft which the Electronic Control Module (ECM) uses to meter fuel delivery.

OPERATION
The TPS electrical circuit consists of a 5 volt supply line and a ground line, both provided by the ECM. By monitoring the voltage on this signal line, the ECM calculates throttle position. As the throttle valve angle is changed (accelerator pedal moved), the output of the TPS also changes. At a closed throttle position, the output of the TPS is low (approximately 0.29 volt). As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be approximately 4.8 volts.

The ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TPS can cause intermittent bursts of fuel from the injector and an unstable idle because the ECM thinks the throttle is moving. A problem in any of the TPS circuits should set either a Code 21 or 22. Once a trouble code is set, the ECM will use an artificial default value for TPS and some vehicle performance will return. A high idle will result when either Code 21 or 22 is set.