Throttle Position Sensor – Working Principle and Applications

Throttle system present in the automobiles monitors and controls the fluid flow in the engine. The power of the vehicle engine can be controlled by changing the air-fuel ratio of the engine which is done by constrictions of the Throttle. The throttle is known as accelerator pedal in cars, thrust lever in aircraft, and as a regulator in steam-powered engines. Modern automobiles operate on the drive-by-wire system. Here, in this system sensors have replaced many mechanical systems in the automobiles. A computerized unit called Engine control Unit monitors the data derived from different sensors and controls the automobile. One of such automobile sensor is the Throttle Position Sensor.

What is a Throttle Position Sensor?

In automobiles, the speed of the engine can be controlled by varying the amount of fuel and air supplied to the engine. For this throttle system is used. Previously, a mechanical linkage was attached to the throttle pedal by which the butterfly valve of the throttle system was controlled. When the driver hits the accelerator cable the valve used to open wide which causes high flow of fuel or air thereby increasing the speed of the vehicle.


In modern automobiles, the Throttle Position Sensor is used for this process. This sensor used to monitor the position of the throttle valve in the vehicles. It can also be viewed as a potentiometer which provides variable resistance depending upon the position of the throttle valve.

Working Principle

This sensor is usually mounted on the throttle body. It senses the position of the throttle valve or butterfly valve and transmits the information to the Engine control unit. This sensor monitors how far down the accelerometer pedal is pushed and gives the output current determining the position of the pedal. The position of the pedal controls the airflow of the engine. If the valve is wide opened, a large amount of air is supplied to the engine and vice-versa.  The output given by this sensor, along with other sensors is transmitted to the engine control unit, which decides the amount of fuel to be injected into the engine accordingly.

This sensor is a three wired potentiometer. Through the first wire, a 5V power is supplied to the sensors resistive layer. The second wire is used as ground whereas the third wire is connected to the potentiometer wiper and provides input to the Engine control system.

Based on its construction, there are three types of throttle position sensors. They are the throttle position sensors with built-in end switches also known as Closed Throttle Position Sensor, the potentiometer type and the combination of both these types.


This sensor gives the engine control unit information about the position of the butterfly valve. It is used to detect the Idle position, Wide Open Throttle state of the valve. When in valve is in Idle state the output voltage of the sensor is below 0.7V. When the full load state is detected the output voltage of the sensor is about 4.5V.

Damage of the Throttle Position Sensor leads to flashing of Check Engine signal. When this sensor is malfunctioned, the computer could not determine the position of the valve correctly which leads to surge or stalling of the vehicle. What are the three states of throttle value the sensor can detect?

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