Older vehicles connected the throttle located on the carburetor by a cable connected to the accelerator in your vehicle. Modern cars are much more intelligent and monitor the power levels and the air-fuel mixtures much more closely.
Many vehicles are now drive by wire systems. These systems need a sensor to provide information to the ECM (Engine Control Module) about the position of the throttle and compare this position to the needs of the motor for power.
This post will cover exactly what a throttle position sensor is, how they work, and the symptoms when it goes bad or fails outright. Can it be repaired, what does a new one cost, and whether they can be reset after a failure will be discussed in this post? These sensors are an integral part of your car’s computer and overall performance.
What is a throttle position sensor?
The throttle consists of a valve or blade which controls the air intake of the engine. An open throttle allows more air into the manifold, while a closed throttle prevents air from entering. The position of the throttle is controlled by the driver as they depress on the gas pedal.
The ECM needs information about the position of the throttle to help manage the amount of fuel delivery to the motor of a car. The throttle position sensor monitors the position of the throttle and reports this information to the ECM.
Furthermore, the ECM uses this information along with other inputs to decide how much fuel to deliver to the motor and the timing of the spark delivered by the spark plugs. Basically, it is one of the most important parts of the vehicle’s fuel management system.
It is mounted on the throttle body. In most cars, if it fails or begins to malfunction, then the ECM will trigger the check engine warning light to turn on and can cause your car to generate a code that can be read with a code reader.
How do throttle position sensors work?
A throttle position sensor consists of mechanical and electrical parts. Inside of the sensor is a mechanical arm that is attached to the shaft that also holds the blade. As the blade moves from closed to open, so does the mechanical arm. This mechanical arm makes contact with a resistive strip creating various voltages as it moves along the strip.
The TPS is connected to a 5-volt supply and a ground wire. The third wire is a signal line that is connected to the ECM. The voltage reported on this signal wire tells the ECM the position of the throttle. Many new systems are beginning to use non-contact systems and also Hall effect sensors to record and report the exact place of the throttle.
The system must be properly calibrated to accurately report the position of the throttle. Otherwise, the engine may not idle properly, stall, and lack power leading to poor transmission shifting.
Symptoms of a Bad or Failing Throttle Position Sensor
Several symptoms may indicate a bad throttle position sensor. As with all faults, they can point to a variety of issues. It is advisable to check the codes generated by the ECM when the check engine light is illuminated, and some or all of the symptoms are outlined below. These are some of the causes and symptoms:
Check engine light coming on
You may have already noticed that your motor is not performing the way it normally does. However, the illumination of the check engine light confirms there is an issue that a sensor has identified. The code on the diagnostic tool will point you in the direction you need to investigate.
If the trouble code indicated the TPS, confirm that the electrical connections are in place and not disconnected. If the engine is lacking power, will not idle smoothly, or stalls, or has difficulty shifting to a higher speed, there may be a malfunctioning old sensor that is causing the problem.
Lacks power when accelerating
While your car accelerates slowly, obtaining speeds beyond 20 or 30 miles per hour may be difficult. Although you are pressing on the gas pedal, the TPS is falsely indicating something different to the ECM and not causing the throttle to open, allowing more air into the combustion chamber.
In addition, because of the erroneous readings, the ECM is not adjusting the flow of fuel to match the power demand. Your car may not shift into a higher gear because there is insufficient power to drive the transmission past a certain speed.
Bad stalling or idling problems
A car may surge in RPM at idle and then die off, even stalling. It may feel that the engine is searching for a steady idle speed but just cannot seem to attain the normal RPM.
You may notice that the engine RPM of the car suddenly fluctuates while in cruise mode, even though the cruise is not calling for additional power. A constant amount of fuel and air is required to maintain an engine at a constant idle level. Your TPS may still be working somewhat but is clearly in the failing stages.
Lack of overall engine power
If this system is sending incorrect data to the computer, the ECM cannot regulate the fuel to air mixture properly. With insufficient air (stuck closed), the fuel-air mixture might be too rich. With too much air (stuck open), the fuel to air ratio may be too lean.
In both cases, the engine lacks sufficient power to perform in the normal manner. Acceleration and higher speeds may not be attainable with the TPS failing in this manner.
Fuel consumption problems
In some situations, the TPS may be gradually failing and provide information to the ECM that is only slightly incorrect. To compensate, the ECM may cause more fuel to be delivered to the intake manifold and combustion chamber.
While the error is not sufficient to cause a trouble code to be generated and the check engine light to illuminate, gasoline consumption may increase. The performance of the motor may be slightly worse than normal as well. This is a more difficult symptom to diagnose since several other faults could be contributing to poor fuel economy as well.
How much does it cost to replace the throttle position sensor (TPS)?
The cost of replacing it can range from approximately $150 to $250, depending on the make and model of the vehicle. Additional factors to consider are the cost of diagnosing the problem since the symptoms could point to several different issues, such as the fuel injection system and other sensors.
The TPS is one of the most important car parts in your engine and should be replaced with high-quality parts. Always ensure that OEM parts are being used to ensure the longevity of the part and performance of your engine after the part has been installed.
How to perform testing on a faulty throttle position sensor?
First, you will need the right diagnostic tool to complete a full report on the status of the TPS. Use a code reader to check the codes that caused the check engine line to illuminate. Note the codes and then clear the codes before restarting the engine. If the codes do not return, you may have an intermittent problem that is more difficult to diagnose.
Next, check the wiring connections for any damage or corrosion. You may want to reset the codes and check to see if they return after this step.
Test for continuity between the TPS sensor terminals. Open circuits indicate a bad TPS. Compare the resistance between the two terminals and compare to the manufacturer’s product spec. If it does not match, you have a bad TPS.
Measure the reference voltage. A low voltage or none at all indicates a wiring issue. Check the ground to confirm the TPS is properly grounded. Measure the resistance as you adjust the throttle flap. If the resistance does not change, the sensor is faulty.
Should I try using a throttle body cleaner?
If you are completing the diagnosis yourself and removing the throttle body and the sensor, use a cleaner to clean the throttle body and the sensor and all dirt and grime. This can be a relatively inexpensive solution compared to replacing the sensor or having a mechanic perform the work for you.
Note that diagnosis is the most difficult part of the job, and cleaning may help improve performance; however, there may be other issues contributing to poor engine performance. Follow the instructions provided by the manufacturer to remove the TPS. Many people will take a picture of the sensor before it is removed to help them with reassembly.
Spray the sensor with cleaner and gently wipe away all dirt and grime. Always ensure there is no cleaner left in or around the TPS before reassembling the sensor. You may want to allow some time for the sensor to completely dry before reassembling and testing the engine.
Can you drive with a failing throttle position sensor?
Driving with a faulty throttle position sensor can cause all sorts of problems for your car, your safety, and the environment. A vehicle that is not performing well due to a faulty TPS may stall in traffic, may be unable to accelerate on the highway, and may lose power at the worst possible time. These issues can be a safety hazard.
Other electric systems in your vehicle may attempt to compensate and be damaged in the process, causing additional repair costs later on. A fuel-rich situation can generate smog that is well beyond the normal emissions tests that your vehicle must pass.
Renewing a license, selling your car, and even trading your vehicle into a dealer can be problematic. At the very least, the value of your vehicle will be lower if it is not operating properly or does not pass an emissions test. Car selling is much more difficult with a faulty TPS sensor.
What happens when you unplug the throttle position sensor?
We are not sure why anyone would want to unplug the sensor. However, if the sensor was unplugged several things are going to occur. First of all, the ECU is not receiving any information about the position of the throttle and will immediately cause codes to be generated and turn on the check engine light.
In addition, the ECU does not have information to properly manage the amount of gas entering the combustion chamber. Your car may run lean or too rich, it may not idle smoothly, and the emissions may significantly increase.
Some modern vehicles are set up to either immediately shut off the car, while others have a limp home mode. This reduces the power but allows the driver to move the vehicle to a repair facility. If you have to have your car towed, then the cost for repairs and the towing charge can become more expensive.
Accelerator Pedal Sensor On Vehicle Models with Electronic Throttle Control
The APS measures the exact location of your foot when pressing on the gas pedals. These sensors are always better than just relying on TPS because they’re more accurate and responsive when you need to regulate speed quickly or if there is an issue with gas efficiency for some reason.
In most cases, the movement data on these car parts are more accurate. If failure is detected, most mechanics will not recommend you to fix these tiny parts. Basically, by checking the resistance values, your mechanics will be able to determine if a replacement is needed.
The throttle position sensor is important in your car’s fuel system, affecting engine performance and emission controls. Gasoline consumption and emissions will also be impacted. A TPS can be replaced by do-it-yourself mechanics. However, proper diagnoses and tools are needed.
If you are trying to remove or install a new one by yourself, remember to disconnect the negative battery terminal first. Also, remember to wear gloves when opening the hood of your car if it was parked outside in the sun. It is not a hard job to do, and you can fix it at any given moment.
Should you replace it or fix it? In most cases, expect a replacement for this car part since it is in charge of keeping your engine running smoothly. A simple repair job will not guarantee that your car will accelerate smoothly or prevent future difficulties when changing gears.