Throttle Position Sensor: Description and Operation

DESCRIPTION
The Throttle Position (TP) sensor is a "three-wire" sensor or potentiometer with a five-volt reference input from the ECM to the sensor, a reference ground from the ECM and a sensor output signal from the sensor to the ECM.

OPERATION
The sensor output signal is an AC voltage that varies with throttle angle. As the throttle 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. As the throttle opens, the output increases so that, at wide-open throttle, the output approaches five volts.

FUEL DELIVERY CALCULATIONS
By monitoring the output voltage from the TP sensor, the ECM can modify fuel delivery based on throttle angle. For example, power enrichment occurs when the throttle angle approaches wide-open throttle. The ECM looks primarily for changes in TP sensor output to control fuel delivery. Acceleration enrichment occurs when the throttle angle increases, similar to an accelerator pump on a carbureted vehicle.

IDLE SWITCH
The TP sensor also houses an idle switch. The ECM supplies both resisted ignition voltage and a ground to the idle switch. When the throttle is closed, the ECM senses the voltage drop caused by the switch closed to ground. The ECM uses this information as a reference for idle air control information.

TP SENSOR CIRCUIT FAILURE
A failure in the TP sensor circuit should set a Diagnostic Trouble Code (DTC) 41 Throttle Position Sensor Circuit.