When you press the gas pedal with your foot, it makes the car move. This is possible when there's the throttle position sensor that helps in reading the amount of fuel needed to deliver to the engine.
And it’s prone to failing and might cause you many problems if you're not watchful. Thus, you need to know the throttle position sensor's failing symptoms and repair advices to make your car OK again.
Functions of a Throttle Position Sensor
A throttle position sensor (TPS) is located on the throttle body under the hood. Being a sensor, it can read how much you're pressing on the gas pedal.
A car's throttle opens accordingly depending on how far you're stepping on the gas pedal. Then, as the throttle opens, it also sucks the surrounding air. As you know from your driving experience, air is needed to oxidize the fuel.
Then, the mix of air and fuel make the vehicle run. In this sense, the throttle position sensor transmits the data read from the position of the throttle body to help the computer or Electronic Control Module (ECM) determine how much fuel to transfer to the engine from the fuel tank.
Another name for the throttle position sensor is potentiometer. A TPS' appearance is T-shaped with a circular dial at the joint. This is a rotating dial and changes depending on the throttle opening. In fact, it has a variable resistor and the TPS has three connections.
One connects to the voltage reference, the second one to the signal of the computer or ECM, and the last to the ground source which is the vehicle’s battery.
What the TPS sends to the computer is the voltage reading depending on the relative throttle position. The sensor can read a maximum of 5 V. Thus, if it reads 2.5 V, it means that the throttle is opened halfway.
This data is sent to the computer and the computer will analyze the information. It will then compute the amount fuel along with other factors such as speed, engine temperature, and vehicle load.
Failing Symptoms of a Throttle Position Sensor
The main reason of the malfunctioning of a throttle position sensor is due to wear. There are many issues associated with it so it's best to learn the failing symptoms to better think of a way on how to approach the problem.
1. Wrong air to fuel ratio
When a throttle position sensor is close to failing, the incorrect mixture of air to fuel for the engine will be the result.
Basically, the TPS' duty is to report to the computer on how many voltages is being carried when the throttle is opened.
If it's faulty indeed, it may even send the wrong signal to the cars' computer which eventually leads to too much or too little fuel for the engine.
A TPS’ function is to feed the computer with correct and consistent data. But if it's malfunctioning, it can send the signal of the throttle being "always open" even if it's not.
This mistake of the sensor creates an overly rich fuel mixture. Another reading which is the "always closed" then results to an overly lean fuel mixture.
This will cause a huge problem in the long run. Wrong mixture can result in poor engine performance. Then, the poor engine performance will be the undoing of your car. This is a severe case when you just had your car for a few years.
2. Check engine light is on
Another tell-tale sign that the throttle position is failing is when the check engine light on the dashboard illuminates. Of course, there are other issues that can cause it to illuminate like the idle air control valve, for example.
3. Engine stalling
Engine idle occurs whenever the car is in a stationary position. Another symptom of a faulty TPS is that there's rough idling. Furthermore, the engine may start to stall. What's more, stalling will not occur at idling but also while driving!
4. Improper acceleration
One of the issues with a faulty TPS is that it won't let you accelerate normally. There's hesitation or delay when you accelerate or even acceleration surge even when you're driving at a low speed without intending it.
5. Idle surging
This can happen when the computer can't tell if the throttle is closed while the car is in an idle position.
6. Bucking and jerking
Unexplainable and sudden bucking and jerking of the car can happen in conjunction with the acceleration issues.
7. Problem when switching gears
If there's trouble when switching gears like when you need to slow down but it doesn't follow, the TPS is likely the culprit. You can be sure that TPS is malfunctioning when this symptom is conjunction with accelerating issues.
Troubleshooting and Repair Advices
As the throttle position sensor is a small plastic device, repairing can be very difficult. Moreover, when a circuit device fails, most likely, you need to replace it with a new one. Fortunately, you won't break the bank when buying a new TPS.
The advices listed below are some of the ways to troubleshoot the throttle position sensor. If they’re no good, then you will have to buy a new one.
1. Use a digital multimeter to check the ground
Since a TPS is basically a circuit, a multimeter is one of the simplest ways to know if it's defective or not. Furthermore, this should be done beforehand before trying to remove it from the car.
The TPS body is connected to a three-way wiring harness plug. The plug should be disconnected so you can do testing.
It is done by pulling the plug from the TPS. Afterward, connect the negative lead (black) of the multimeter to the negative terminal of the battery. The battery is the ground source.
As mentioned, the throttle position sensor connects to three parts. The connector that connects the TPS to the ground source (battery) is usually at the rightmost side.
This is the first part to check to make sure that there's enough current flowing from the battery to the circuit device.
Set your multimeter to a DC voltage scale. Then, turn the ignition key to the ON position but don't start the engine. You might be electrocuted. Next, insert the red lead (positive) of the multimeter to one of the terminals in the three-way wiring plug.
The correct terminal that connects to the ground will then read 5 V. One of the terminals should read 5 V while the other two should read 0 V.
However, if none of the terminals reads 5 V, this means that the TPS can't connect to the ground. Thus, this is the root cause of the TPS problem. Either that there's physical damage to the wire connecting the throttle body to the battery.
In this case, check for damage after turning the ignition key back to OFF position.
2. Backprobe the throttle position sensor
After testing for the reference voltage (the terminal reading 5 V while the other two read 0 V), next step is to backprobe the sensor. Just reconnect the wire harness plug back to the sensor.
The orientation of the multimeter will be different from the previous. The black lead will connect to the reference terminal voltage of the ground which was what we identified in the previous test while the red lead of the multimeter will connect to the signal wire of the plug.
However, the leads will not directly be inserted to avoid damage to the wires. In backprobing the sensor, use long thin steel wires with makeshift ring ends as hooks to insert into the signal connector and the ground connector. The hook ends of the steel wires will then carry the multimeter leads.
Turn on the ignition to the ON position again and don't start the engine. Next, make sure that the throttle body linkage is closed.
Now, read the multimeter. It should display about 0.9 V. Exact reading may vary depending on the car make and model.
While the multimeter leads are still connected, turn the throttle position slowly but gradually into an open position. Have another person press on the pedal or you can have the multimeter face you while you're in the driver's seat.
While opening the throttle, observe how the reading on the multimeter display changes. In normal circumstances, the reading should gradually increase up to a maximum of about 5 V.
A faulty or defective TPS would have a sudden spike to 5 V. This is the case when the reading is stuck to a certain voltage until it shoots up. Also, the TPS will need replacing when the multimeter reading didn't reach 5 V; like short of 1 V.
The obvious implication here is that the computer may have a hard time in processing the data taken from the throttle position sensor. For instance, though you're opening the throttle body slowly, the computer will read it as a sudden pressing on the gas pedal.
This means that the physical resistive component of the TPS has worn away with time. If it's worn, the sensor should not be used.
3. Use scan tools
Another easy way to scan if there's defect on the TPS is using an automotive scan tool. For vehicles made in 2006 and onwards, use an OBD II scanner. Otherwise, if it's prior than 2006, then use OBD I.
You connect the device to the dashboard and a stream of data will appear on the screen. These are all error codes. Then, these error codes can explicitly or implicitly tell if the throttle position sensor is getting bad.
4. Clean the throttle position sensor
This is what you will likely do when there are no problems with the digital multimeter method. A dirty throttle position sensor results from the buildup of crankcase vapors as it's located at the throttle body. The oily residue can be cleaned with an automotive cleaning solution.
First, start the engine and have it stay in idle for several minutes. This heats up the engine temperature and makes the grit and debris easier to clean later.
Then, turn it off. After several minutes, open the hood and disconnect the wire plug connecting the TPS to three connections. Next, proceed to remove the TPS using wrenches or drivers to remove the bolts or screws.
Using a clean rag, put a significant amount of cleaning solution and dab it on the TPS. Rub the dirt off until you see no more grit.
Be careful not to put liquid into the electrical component as it may render the TPS defective. On the sensor part, just use the dry rag to rub it until it becomes clean.
After that, with a dry and clean rag, remove the moisture on the surface of the TPS until it is clean. Finally, put the TPS back in its original place. Attach the bolts/screws to the TPS and reconnect the wire plug.
5. Replace the throttle position sensor
The last and logical step to follow after testing the methods above and to no avail is to replace the TPS with a new one. The price varies from $30 to more than $100 depending on the car make and model.
If you're having trouble on how to replace it, it's best to leave it to the mechanic. The mechanic will perform a software re-programming if there's a need.
This is in order for the new TPS to match with other management software of the car's engine. Furthermore, the mechanic will also wipe out the trouble codes left by the old TPS.
The throttle position sensor's existence is significant for your driving and car’s safety. It also preserves the fuel economy and efficiency because it instructs the computer on how much fuel to use. Thus, when it becomes faulty, it can affect a lot of vehicle parts and they would exhibit poor performance.
It will indeed be a great help when you know how to determine the failing symptoms of a throttle position sensor and the ways to troubleshoot it. That way, you can replace or repair the problem right away.