Throttle Position Sensor: Description and Operation

The TP Sensor is connected to the throttle shaft on the Throttle Body Fuel Injection unit. It is a potentiometer with one end connected to 5 volts from the ECM and the other to ground. A third wire is connected to the ECM to measure the voltage from TP Sensor. As the throttle valve angle is changed (accelerator pedal moved), the output of the TP Sensor also changes. At a closed throttle position, the output of the TP Sensor is low (approximately .48 volt). As the throttle valve opens, the output increases so that, at Wide Open Throttle (WOT), the output voltage should be approximately 4.5 volts.
By monitoring the output voltage from the TP Sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). If the sensor CKT is open, the ECM will set a DTC 22. If the circuit is shorted, the ECM will think the vehicle is at WOT, and a DTC 21 will be set. A broken or loose TP Sensor can cause intermittent bursts of fuel from the injector, and an unstable idle, because the ECM thinks the throttle is moving. Once a DTC is set, the ECM will use an artificial value for TP Sensor, and some vehicle performance will return. This will also affect automatic transmission performance.