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Symptoms Of A Bad Throttle Position Sensor

Nidhi Nangia
By Nidhi Nangia. Updated: June 17, 2020
Symptoms Of A Bad Throttle Position Sensor
Image: holley.com

Throttle position sensor, or TPS, is responsible for transmitting information about the throttle’s position to the ECM or Electronic Control Module. It contains a number of mechanical parts that can become damaged and worn out with time and usage. In these cases, it will require an immediate repair or replacement. A bad throttle position sensor starts malfunctioning and relays wrong data to your car’s automated system. As a result, it usually leads to poor fuel efficiency. Knowing the signs of a bad throttle position sensor will help in quickly diagnosing the issue and making the required amendments in time. Read this oneHOWTO article to know about the symptoms of a bad throttle position sensor so you can do just that.

  1. Importance of a good TPS
  2. Symptoms to look for
  3. Conclusion

Importance of a good TPS

The throttle position sensor detects the position of your gas pedal (sometimes known as accelerator or throttle) and sends its information to your car’s engine control unit. Here, this information is used to control the throttle body which forms an integral part of the air intake unit. If your sensor is not working properly, the engine will misread the ratio of the air and fuel in your vehicle and the car will cease to run smoothly. This is why it is important to keep your TPS in good working condition, as it ensures your vehicle gets the most out of the fuel it uses.

Symptoms to look for

Service light turned on

This is perhaps the first thing you will notice in your vehicle. Although service lights can indicate a number of issues with your vehicle, this may mean a faulty TPS. Try to find out why your service light is turned on. If it’s due to a bad TPS, then it is advised to take your car immediately to the mechanic. He will confirm the issue and take the best steps to resolve it professionally.

Diagnosis on the digital multi-meter

Throttle position sensors will usually have three wires coming out from it. First is for constant reference voltage, second is for ground and the third is for sensor output in the middle. Connect the ground wire with the battery ground and turn on the key. When you probe the wires, you should get a steady voltage of around 5 volts. If not, then there is definitely some problem with your throttle position sensor.

Late acceleration

One of the sure signs of a bad throttle position sensor is a slight delay in your car’s acceleration. When you press your gas pedal, the car should accelerate immediately. If there is a delay between these actions, you should take your car to the mechanic. In addition, if you notice a little stumble in your vehicle while accelerating, then bad TPS is certainly a possible reason reason.

Unexpected stalling

Another sure sign of a bad TPS is unexpected stalling, no matter if you are driving the car or idling. Stalling can be a sign of some other issues as well, but if you notice this along with the other symptoms described here, then you can directly relate it to the bad throttle position sensor. Bad TPS can give wrong information to the engine, causing it to stall without any warning. If the problem persists and occurs frequently, then you have no other option but to replace the sensor.

Problematic drivability

Throttle position sensors receive most of the wear on the skinny part of their crescent resistor. This is the part where the current meets most of the resistance. Jerky movements while accelerating is a classic symptom of a bad throttle position sensor. A faulty TPS will result in unsteady mechanical connection instead of total failure. Due to this false information, the computer will detect that you are frequently closing and opening the throttle, even if you are not doing so. The oxygen sensor will indicate the wrong air-fuel ratio to the computer and will not be able to adjust to the delivery of fuel fast enough. As a result, you will notice rapid fluctuations while idling and a kind of stutter when you accelerate.

Symptoms Of A Bad Throttle Position Sensor - Symptoms to look for
Image: Location of throttle, the sensor is just out of view at the top.

Automatic increase in speed

If you see that your car’s speed increases automatically on its own, especially when you drive it on a highway, then you should immediately consider taking it to a professional mechanic. This can be a sign of a bad TPS and can lead to dangerous situations while on road. This happens because the butterfly valve present in your throttle closes up and pops open suddenly when you push the throttle harder.

This happens because the sensor is not able to detect the throttle’s closed position. You may also notice a jerking and bucking movement in your car when you accelerate. A bad throttle position sensor will not be able to give proper information to the on-board computer, due to which it will not detect the engine’s performance at the optimum level. In the lack of proper input, the engine will function erratically and prevent the car from running smoothly.

Faulty output reading

At idle, your car’s output reading should be less than 5% of your reference voltage and over 90% when the throttle is wide open. So, if you see a reference of 5 volts, you should get it 0.25 at idle and over 4.5 at full throttle. Slowly sweep it back and forth and check if the voltage remains steady at these positions. If the numbers or the meter jumps rapidly, it is an indication of a bad TPS. Similarly, if the output voltage is over 5% at idle and below 90% at wide open, then it is a common symptom of a faulty throttle position sensor.

Particular codes

The computer system of your car will identify an awry issue with your TPS and send a code to notify the driver. There are so many codes to indicate a bad throttle position sensor, ranging from 120 to 229. If you receive any of these self-diagnostic codes, you can be sure that something is wrong with your TPS. Many modern scanners can monitor the position of your car’s throttle in real time while the engine is running. It can detect the sensor circuit fluctuating rapidly and will display any changes in the voltage. A scanner can update its readings after every 0.1 second and this time is enough to monitor any voltage fluctuations.

Difficulty switching gears

If your throttle position sensor is not working properly, it will not report the position of the accelerator. As a result, you will find it difficult to change gears while slowing down or speeding up. While this can also be a sign of a faulty transmission system, you can be sure of a bad TPS if it is coupled with other signs as well.


If you want to identify a problematic throttle position sensor, then there are more than one ways to find it out. Using a multi-meter is a sure-shot way of determining the issue, but the process may get a little complicated. One symptom can be a sign of several other problems as well. We have summed up some of the easiest and surest ways of diagnosing TPS related problems. You can even use an automotive scanning tool to display a stream of data with which you can identify the problem and get it resolved by a professional.

If you want to read similar articles to Symptoms Of A Bad Throttle Position Sensor, we recommend you visit our Car Maintenance and Repair category.

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Saurabh Singh
My Ford fusion 1.6 ltr petrol on driving all of a sudden accelerator stops working and the vehicle runs on aconstant rev or acceleration which in return achieves a maximum speed of 30 km per hr while meter frame indicates EAC fail
Image: holley.com
Image: Location of throttle, the sensor is just out of view at the top.
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Symptoms Of A Bad Throttle Position Sensor