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Throttle Position Sensor Function

Throttle Position Sensor Function

What is a throttle position sensor? What is its prime function? What are the symptoms that mark a faulty one? Read to find all the answers.
Omkar Phatak
Today's cars are monitored and their internal systems are controlled by embedded computers. While driving cars is considerably simpler with automatic transmission and inbuilt automated control systems, it has become increasingly difficult to attempt car repairs on your own. The engine control unit and its internal electronic circuitry is so complicated that car problem diagnosis is a tough job for most. The throttle position sensor (TPS) is one component in the internal monitoring and feedback mechanism of the engine control unit (ECU).


The engine control unit does all the decision-making for a modern car. To make decisions, it needs live data or feedback regarding the current status of a car's working. This function is done by sensors fixed at various positions inside the machinery, where they record and send information, back to the engine control unit, through electronic signals.

One such device is the throttle position sensor. As its name suggests, this sensor continuously monitors throttle position and sends feedback to the ECU. The throttle is a valve that controls the quantity of air taken in by a petrol engine. It decides how much air an engine 'breathes' in.

As a driver steps on the accelerator pedal, the throttle opens wider and provides more air. The quantity of air taken in, decides the rate of fuel burning and the power delivered by the engine. The electronic fuel injection systems, fitted in cars, are controlled by ECU. According to the sensor's data, the ECU must decide how much fuel needs to be injected in an engine, during every cycle. The timing of fuel injection and fuel ignition, depends on the sensor's output.

Thus, the amount of fuel injected, changes according to the air made available for combustion, to achieve maximum efficiency. The sensor is a variable potentiometer that sends voltage signals, that are directly proportional to air intake quantity, which in turn depends on the throttle position.

When the throttle is almost closed, the signal is low and it rises as the throttle opens wider. If the sensor fails, there is a break in synchronization of the engine cycle, causing problems. The sensor is generally located near the throttle body and can be easily spotted on either its right or left hand side, under the car hood.

Symptoms of a Bad Sensor

Knowing these symptoms will help you in taking care of the problem, well in advance, before the situation deteriorates further.

Rough Engine Performance
If you find that your car's engine is not quite smooth in its overall performance, the culprit might be a sensor that has not been calibrated properly. Resetting the sensor will take care of the problem.

Problems With Acceleration
When this sensor has gone bad, the engine control unit is blind to throttle position. Hence, there is a break in the otherwise synchronized working of the fuel injection process, during every engine cycle . You realize that the car does not accelerate, as it should, when you step on the pedal. In such cases, it is important that you get the sensor checked, as soon as possible.

Intermittent Idling
The car idles intermittently and does not quite respond to your acceleration control. This is a classic sign of a sensor connection gone loose or its malfunctioning. Immediate action must be taken to prevent drop in engine efficiency.

Troubleshooting this car part, is best left to professional car mechanics as the internal mechanism is too complicated and delicate for any amateur to handle. However, the symptoms of a bad sensor, mentioned above, can help you identify the problem. Even though you may not be able to carry out repairs on your own, it helps to know the symptoms of a developing car problem before it takes a more serious turn.