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Fuel System Home Page > Parts of the Fuel/Engine Management System > Throttle Position Sensor

Function: Electronically informs the PCM of the throttle's angle. The PCM uses this input to regulate the fuel and ignition system.

Signs of Wear: "Service Engine Soon" illuminates, poor engine performance.

The throttle position sensor, or TPS, is located near the throttle body in the engine compartment. It normally has three wires connected to it. One wire supplies the TPS with 5 volts -- usually coming from the computer. The center wire is the signal wire, sending the throttle position back to the computer. The third wire is an electrical ground. The circular strip within the TPS is a variable resistor.

In the idle position, the arm on the sensor is at the position of greatest resistance on the circular strip, resulting in a small voltage signal being sent to the engine computer. When the throttle pedal is pushed, the sweeper arm moves across the resistor strip, decreasing the resistance in the circuit. As the resistance drops, the voltage signal to the ECU increases.

Throttle position is an important input; the engine computer uses it to calculate how much fuel such be sprayed into the cylinders, and also precise time that the spark plug should ignite the fuel.

Repeated sweeping of the resistor arm can eventually lead to "dead" sections in the resistor. When a dead-spot develops, the engine computer does not receive a TPS input at specific throttle positions and is unable to correctly determine fuel delivery and ignition timing. This can cause the engine to stumble on acceleration and will usually cause the check engine light to illuminate.

Have your vehicle fuel and engine management system checked by an ASE Certified Technician in Fuel System Services. Schedule service today to visit our repair facility on the southwest of Houston.

Throttle Position Sensor - Houston's Premier Auto Repair Facility