Throttle Position Sensors (TPS) are just one of the many sensors on board your car. As the name implies, the TPS measures the position of the throttle blade. Older vehicles have one TPS, whereas modern vehicles with electronic throttle control (ECT) feature two TPS as a redundancy for a fail-safe.
The TPS is a fairly simple component of the vehicle, but failure of the TPS can lead to several recognizable symptoms.
What Is A Throttle Position Sensor?
The throttle position sensor monitors the position of the throttle valve (or blade) which allows air into the engine’s intake manifold. The amount of air that reaches the engine is determined by how far down the accelerator pedal is pushed on, which dictates how far open the throttle valve is opened.
When the throttle valve is fully open, then a large amount of air flows into the intake manifold. The narrower the opening is on the throttle, the less air will flow into the intake manifold.
The throttle position is reported back to the engine control module which uses throttle input in conjunction with the other vehicle parameters to determine how much fuel is injected into the engine and what the timing is for the ignition cycle.
The throttle position sensor is typically mounted on the throttle body (the piece that houses the throttle valve).
When the throttle position sensor fails, the engine control does not know what the throttle position is; it is often results in a “check engine warning light“, or a rough, surging, hesitating or stalling engine (due to inability to set fuel mixture or ignition timing properly).
Key Takeaway:
- The throttle position sensor (TP) determines the position of the throttle blade.
- If a TP sensor has failed, it will show clear symptoms to the driver: check engine light on, engine and transmission issues, and limp mode.
- Diagnosing a defective TP sensor is easy. You have to test the part. Always check for diagnostic trouble codes first, and if everything is fine, use a digital multimeter and test the sensor.
How a Throttle Position Sensor Works
Every internal combustion engine has a throttle body (or butterfly valve) located between the intake manifold and the air filter.
The purpose of the throttle is to allow air to enter the engine. When you step on the gas pedal, you push the throttle open, and more air needs to enter the internal combustion chamber of the engine.
As the air enters the engine, more fuel is injected, and it is the ignition of this air/fuel mix that makes engine power.
The throttle position, or how open the throttle is, determines how much air gets into the engine. The fuel management system has a throttle position sensor that monitors the throttle position.
When you request the car to go faster, the throttle position sensor sends the throttle position to the engine control unit, and the engine control unit controls the throttle so that the appropriate amount of air can enter the engine, based on how fast you want to go.
The gas pedal does not control the throttle; it sends throttle position to the engine control unit. When you push down on the gas pedal, you are telling the engine control unit to open the throttle more.
The more you press down on the gas pedal, the wider the throttle will open to allow more air to enter the engine. More fuel will be injected into the engine cylinders to ensure proper ratio for combustion.
Symptoms Of A Bad Throttle Position Sensor
If you have a throttle position sensor that is bad, then the ECU will no longer know the position of the throttle. When this happens, the ECU will not be able to control the amount of air to be delivered into the engine to create combustion. This ultimately will interfere with how the vehicle drives and can interfere to the level of no longer being safe on the road.
You will notice the indicators that you have a faulty TPS pretty quickly once it is damaged or worn out. While initially you may not associate the TPS to be the reason for the indicators, you’ll want to take notice of these symptoms to assist in determining further or obtaining a proper diagnosis.
#1. Rough Idling.
When you are idling in the vehicle, the throttle position should be very static, allowing an open throttle gate slightly enough air to allow the vehicle to idle. Rather than being steady, the throttle may exhibit fluctuations.
The throttle will open and close slightly instead of remaining in a stable position. When you start to notice that your vehicle is idling roughly, rough, or sputtering, you may want to consider a faulty Throttle Position Sensor.
#2. Check Engine Light Is On.
A check engine light can signify many different issues, and a faulty TPS is one of them. The TPS on your vehicle controls how much air enters the intake manifold of your engine. A bad TPS will either have too much or not enough air.
There are a few sensors in different areas of your vehicle that also measure air such as the mass airflow sensor. If the readings are outside of the range of normal for the readings, the check engine light will illuminate.
You should take your vehicle to an automotive repair shop using a scan tool to read the trouble codes in the ECU and to assist in determining if the TPS could have been responsible for your check engine light being illuminated.
#3. Regular Engine Stalling.
This symptom is probably the most hazardous to the driver. If the TPS is not providing the enough opening of the butterfly valve in the throttle while driving, it will cause your car engine to stall.
The throttle position sensor will also impact the fuel delivery system in your vehicle. The TPS may not deliver enough fuel, and this can also stall the vehicle as well.
If this has happened regularly, you need to have a mechanic check your vehicle to determine if the TPS may be faulty.
#4. Bad Fuel Economy.
If your throttle body sensor is bad, it could affect the air/fuel ratio in your vehicle, thus causing it to burn more fuel. If the sensor is reading incorrectly, then it is sending the signal to the fuel pump that too much fuel is needed, and the injectors are injecting too much fuel into the intake.
The fuel pump and injectors are injecting more fuel than the vehicle needs, which is totally wasteful. The vehicle does not need this much fuel, but since the (faulty TPS) sender reading incorrect data, the vehicle thinks that it needs it.
When your fuel consumption is at a time where you do not have any proposer reason why it is going up, it is a good time to check the TPS for failure.
#5. Limp Mode Activated.
Your car’s computer is extremely talented, and can typically detect issues with your vehicle fairly rapidly. If it detects that there is a problem with your TPS, it may place your vehicle in limp mode. This will restrict your timing to slow the ignition, which will cause a reduction in overall engine performance.
This is purely a mode that allows you to not cause damage to your vehicles engine. You can drive the vehicle home, or to a garage for repair, but all performance features and stability control have been disabled.
Whenever your vehicle is in limp mode, you should check with a mechanic immediately.
#6. Gear Shifting Issues.
Believe it or not, the automatic transmission uses information about your throttle position to identify when to change gears. It also studies throttle position data to determine how hard it needs to shift. If the TPS is faulty, it could send incorrect data to the transmission, causing issues when shifting gears.
You may notice that your car is shifting too early in the trip, or you do not feel it shift into the next gear on time. If you believed you need a transmission repair when there was an issue with you throttle position sensor, that would be a possibility.
#7. Poor Engine Performance.
When you push the accelerator to the max on your truck, you expect it to respond quickly. If it doesn’t, it could be that the throttle valve isn’t opening enough, and it probably has something to do with a faulty TPS.
If you find that you have to push harder on the throttle to get the same amount of performance from your engine then now is a good time to test your TPS. It may be a malfunctioning part, which results in not allowing your throttle to open as it should.
#8. Jerking Or Bucking Of Vehicle.
This is a very obvious symptom. When the throttle position sensor fails, it usually results in your car bucking or surging while you drive. This is occurring because of the TPS outputs wildly varying readings, which is causing your RPM to haven’t a tug-of-war battle between high and low.
The constant rising and falling of your RPM levels will also cause a bucking of your car while you drive and may mask a slipping transmission. This situation is annoying, and it could possibly dangerous.
You should not drive any further and take the car to a mechanic.
How to Test the Throttle Position Sensor?
If you own a multi meter, testing a TPS on your passenger vehicle is a pretty simple procedure. The following is a step-by-step how to test a TPS sensor.
#1. Locate the throttle mechanism.
The housing attached to the engine compartment will stay as is. It will be the outlet branch line from which the fuel line branches off from the fuel rail.
There will be a device attached to the throttle body with the cables leading to the ECU. That is the throttle’s position sensor.
#2. Locate the wires leading from the power source, ground, and signal.
After you have identified the components, the next step is to locate the power, ground, and signal wires.
Simply said, this is because all cars follow the same colour scheme. The black wires represent the ground, red wires represent the power. The signal wire will be of different colours: green, yellow, or blue.
#3. Check the reference voltage.
Set the dial on the multi meter to read volts. You will need to check the voltage referring to as reference. This shows the voltage passing between the TPS and the ECU.
To check that the TPS is operating correctly, take the negative probe of the meter and place it on the positive tab on the TPS wire, then take the positive probe and place it on the negative tab. If everything is working correctly, the meter reading should have been around 5 volts.
#4. Checking signal voltage.
At this point you need to check the voltage signal. To do this you proceed to take the positive probe and connect it to the signal wire tab, and then take the ground probe and connect it to the frame of the vehicle. A reading of a half volt would be acceptable.
How Much Does it Cost for a Throttle Position Sensor Replacement?
An engine will need the right amount of air just as much as it needs the right amount of fuel. Failing to get the required amount of air for its internal combustion process will result in inadequate power generation and a myriad of other issues.
And eventually, you’ll have no choice but to obtain a diagnostic check from a licensed mechanic. If it turns out your throttle position sensor is faulty, you’ll need to replace it right away.
The average cost of the throttle position sensor is between $110 and $200. Parts cost between $75 and $105, and labor costs between $35 and $95. You will also need to figure in any additional fees and taxes that will get tacked on.
Overall, you should not have to pay over $250 to have this replacement completed. Additionally, you may be able to negotiate a cheaper hourly rate by searching for a more reasonable mechanic.
A. Range
You can expect to spend about $150 -$710 to replace the throttle position sensor (TPS), which consists of:
- Parts cost: $100 to $540
- Labor Cost: $50 to $170
NOTE: If you happen to drive an older vehicle that has an older mechanical throttle system (no drive-by-wire throttle), the sensor is removable, and the replacement costs less.
For a modern vehicle, the TPS is integrated with the throttle body. In this case, the throttle body must be replaced, which incurs a greater cost.
B. Factors Affecting Costs
A few additional reasons that may change your total include:
- Sensor type: Potentiometer-based sensors are common for older vehicles. Newer vehicles typically use Hall-effect-based sensors. Hall effect sensors are more modern and hence more expensive, so their expenses would be steeper.
- Service complexity: On older vehicles, the TPS is usually a fixed switch on one side of the throttle body (throttle valve spindle). It was very easy to get the TPS removed. On a drive-by-wire vehicle, the TPS sensor is integrated with the throttle body housing so the throttle body has to be replaced at the same time. Since part of replacing the throttle body is the added complexity, the labor costs would be more.
- Recalibration cost: Sometimes the recalibration of the sensor is included in the replacement cost, but if it isn’t, you will have to spend an additional $100 to $200 to calibrate it upon replacing the TPS.
Common Misdiagnoses of TPS (When It’s Not the TPS to Blame)
Throttle position sensor symptoms can be misdiagnosed, and you can recognize these common misdiagnoses and possibly save yourself a lot of frustration and money.
- Mass Airflow (MAF) Sensor Failure – The MAF sensor measures the air intake too, and will exhibit similar symptoms to TPS issues. They both can cause poor acceleration and rough idling but ultimately MAF problems will not cause the sudden acceleration changes we see with TPS failure.
- Vacuum Leaks – A vacuum leak can cause erratic idling and poor performance. Both of these will be very similar to TPS issues. However, there will usually always be a hissing sound that accompanies a vacuum leak that isn’t associated with a TPS problem.
- Fuel Injector – If you have blocked/down fuel injectors you would also see symptoms like rough idling or bad acceleration which you might mistake for TPS problems. However, fuel injector problems will generally not cause the check engine light to come on as quickly as TPS problems.
- Ignition System – Any type of ignition problem, from the spark plugs, the coils or the wires, can cause misfires. You might mistake a misfire for jerking associated with TPS failure. However, ignition problems usually display more consistent symptoms across all driving conditions.
- Catalytic Converter – A clogged catalytic converter can cause lack of power and horrible fuel economy similar to the TPS issue. However, catalytic converter problems generally worsen over time and TPS issues typically come on suddenly.
Electronic vs Mechanical Throttle Position Sensors
Throttle position sensors have two main types (mechanical and electronic). The electronic version is sometimes termed a “drive-by-wire” system. Here is a breakdown of both types:
| Feature | Mechanical TPS | Electronic TPS |
|---|---|---|
| Connection | Physical cable | Electronic signals |
| Sensor Type | Potentiometer | Hall effect or optical sensor |
| Design | Simpler | More complex |
| Precision | Less precise | More precise |
| Response Time | Slower | Faster |
| Durability | More prone to wear | Generally more durable |
| Maintenance | May require adjustments | Less frequent maintenance |
| Diagnosis | Generally easier | Can be more complex |
| Integration | Limited | Easily integrates with other systems |
| Failure Mode | May allow some manual control | Often has electronic fail-safe modes |
The Bottom Line
The throttle position sensor is an important part of your car’s fuel management system. Defective TPS sensors can cause strange issues and can even be dangerous.
You might notice that the car doesn’t accelerate when you press the pedal, or it might start bucking and surging. Either way, you should have the issue fixed before it becomes too much of a problem, and the repair is usually not overly costly.