Throttle Position Sensor: Testing and Inspection

The throttle position sensor (TPS) changes position as the throttle valve angle changes. The TPS is a potentiometer, mounted in the carburetor, with one end connected to 5 volts from the ECM and the other end to ground. A third wire is connected to the ECM to measure voltage from the TPS. At a closed throttle position, the output of the TPS is approximately .5 volts, but will vary with application. As the throttle valve opens, the output voltage increases so that at wide-open throttle the output is approximately 5 volts.

If the TPS is out of adjustment, idle quality may be affected and performance may be poor. If the TPS circuit is open, the ECM will think the vehicle is at wide-open throttle, and cause the ECM to go full rich, and set a Trouble Code 21. Refer to Computers and Control Systems / Testing and Inspection / Diagnostic Charts.