Throttle position sensor is a sensor used to monitor the position of the throttle in an internal combustion engine. Throttle position sensor is usually located on the butterfly spindle so that it can directly monitor the position of the throttle valve butterfly. Throttle position sensor is usually a potentiometer, and therefore provides a variable resistance dependent upon the position of the valve (and hence throttle position).

Throttle position sensor signal is used by the engine control unit (ECU) as an input to its control system. The ignition timing and fuel injection timing are altered depending upon the position of the throttle, and also depending on the rate of change of that position. Some ECUs also control the throttle position and if that is done the position sensor is utilised in a feedback loop to enable that control.

Types of Throttle Position Sensors

  • Wireless (non-contact type) throttle position sensors work on the principle of Hall effect, wherein the magnet is the dynamic part which mounted on the butterfly valve spindle and the Hall effect sensor is mounted with the body and is stationary. When the magnet mounted on the spindle which is rotated from zero to WOT ( wide open throttle), there is a change in the magnetic field for the Hall effect sensor. The change in the magnetic field is sensed by the Hall effect sensor and the voltage generated is given as the input to the ECU.
  • Potentiometric type throttle position sensors, which has two metal parts are in contact with each other, while the butterfly valve is turned from zero to WOT, there is a change in the resistance and this change in resistance is given as the input to the ECU.

Failure Analysis & Symptoms of Bad Throttle Position Sensors

Symptoms of a Defective Throttle Position Sensor

Following is a list of symptoms, either of or a combination of which, a car driver may experience because of a defective throttle position sensor:

  • Bucking and jerking of the car
  • Idle surging
  • Sudden stalling of the car engine
  • Hesitation while the driver of the car is trying to accelerate
  • Sudden surge in car’s speed while driving on the highway

What Happens with bad Throttle Position Sensor?

The data provided by TPS is invaluable for proper startup, idle and easy throttle response of the car. These operations are affected when a bad throttle position sensor feeds erroneous data to the car’s computer because of which the:

  • Engine malfunction indicator light (MIL) is turned on
  • The driver of a car experiences difficulty while changing gears.
  • The fuel economy of the car drops drastically.
  • Causes difficulty in setting base-ignition-timing of the car