Throttle Position Sensor (TPS)
The Throttle Position Sensor (TPS) is a "3 wire" sensor or potentiometer with a 5 volt reference input from PCM to sensor, a reference ground from PCM to sensor, and a sensor output signal from sensor to PCM. See Fig 1 . The sensor output signal is a DC voltage that varies with throttle angle. As throttle valve angle is changed (accelerator pedal moved), output of TPS also changes. At a closed throttle position, output of TPS is low (approximately .5 volts). As throttle plate opens, output increases so that, at wide-open throttle, output voltage should be approximately 5 volts.
By monitoring output voltage from TPS, PCM can modify fuel delivery based on throttle valve angle. For example, power enrichment occurs when throttle angle approaches wide open throttle. The PCM looks primarily for changes in TPS output to control fuel delivery. Acceleration enrichment occurs when throttle angle increases, similar to an accelerator pump on a carbureted vehicle.
The TPS can either be misadjusted, open, or shorted. If sensor is open, PCM will think throttle is closed, and performance will be reduced. This will normally set a Trouble Code E022. If switch is shorted, PCM will think vehicle is at WOT, and a Trouble Code E021 should be set. Once a Trouble Code is set, PCM will substitute a value for TPS, and some vehicle performance will return.