Your car has dozens of sensors onboard—one of which is the throttle position sensor (TP). As you might have guessed, the TP sensor measures the position of the throttle blade.
Older vehicles have just one TP sensor, whereas newer models with electronic throttle control (ECT) have two sensors as a fail-safe measure.
Although the TP sensor is a relatively simple part, it can cause several noticeable symptoms if it fails.
The TP sensor is a potentiometer—a device that changes resistance (and therefore, voltage) in response to an adjustment knob or terminal. In the case of the TP sensor, the resistance changes in response to the movement of the throttle shaft.
Typically, most single TP sensors have an output voltage range between 0.5 volts (throttle closed) and 4.5 volts (throttle wide open).
But in an ETC system that uses dual TP sensors, the output from one sensor is inversely proportional to the other. That means, one sensor will read 4.5 volts when the throttle is closed (and 0.5 volts when the throttle is open). The other sensor will read 0.5 volts when the throttle is closed (and 4.5 volts when the throttle is open).
Your car’s primary computer, which is also known as the powertrain control module (PCM), uses the TP sensor signal in a variety of ways. For example, the PCM uses the input from the sensor when calculating ignition timing, fuel delivery, and automatic transmission operation.
Common throttle position sensor symptoms include:
The PCM monitors the TP sensor to ensure its working properly. If the module perceives a problem with the TP sensor or its circuit, it will turn on the check engine light.
As was mentioned, the TP sensor is an input to the PCM for fuel delivery, ignition timing, and other outputs. Therefore, problems with the TP sensor can easily lead to engine performance problems, such as:
Because the TP sensor is an input to the control module for various automatic transmission functions (e.g., shift points and torque converter clutch operation), a problem with the sensor can cause transmission performance issues.
For example, you might experience harsh or delayed shifting.
Modern vehicles with ETC use a pair of TP sensors as one of the primary inputs for throttle control. If one of the sensors fails, the control module will likely put the vehicle in “limp mode” or “reduced power mode” as a fail-safe measure.
You can test a throttle position sensor with a digital multimeter (DMM), a scan tool, or an oscilloscope.
Using a DMM is the method most DIYers are comfortable with. The following steps will give you an idea of what the troubleshooting process typically involves.
Note: The following are general guidelines for educational and entertainment purposes only. Consult your vehicle’s factory information for specific repair instructions and recommended safety procedures.
Is there a diagnostic trouble code (DTC) for the TP sensor stored? Then there’s probably a problem with the TP sensor or its circuit.
In most cases, cars built after 1996 with onboard diagnostics (OBD) II will set a code for a bad TP sensor. Many older cars with OBD I will also set a DTC when there’s a problem with the TP sensor. You can check for diagnostic trouble codes using a scan tool or code reader.
But keep in mind: TP sensor codes don’t necessarily mean the sensor is bad. You’ll need to do some troubleshooting to rule out problems elsewhere in the circuit.
If you find TP sensor-related codes stored, you can move on to performing a visual inspection. You’ll want to look for issues, such as damaged wires and poor connections.
Repair any problems found, then clear the DTCs, and see whether the problem returns.
Next, if you didn’t find anything obvious during the visual inspection, you’ll want to test the TP sensor with a DMM. In most cases, the TP sensor will have three wires going to it: reference voltage (from the PCM), return signal (from the sensor), and ground.
Here’s how to test the reference and ground portions of the circuit:
If you find both sides of the circuit to be okay during testing, you can move on to checking the TP sensor itself. On the other hand, if your test results indicate a circuit problem, you’ll need to trace the factory wiring diagram and repair the issue as needed.
Note: This test will not work on a vehicle with electronic throttle control. It only applies to vehicles with a traditional, mechanical throttle body.
If the TP sensor does not respond correctly to the test mentioned above—and you’ve already ensured the circuit is intact during step #3—the sensor is likely faulty and needs to be replaced.
Before condemning the sensor, however, it’s wise to inspect the throttle body for binding and excessive carbon buildup. Issues, such as these can prevent the TP sensor from reading properly.
Here is an excellent video that outlines the TP sensor testing process:
You can also choose to remove the TP sensor from the vehicle and test it as outlined in this video:
Driving with a bad throttle position sensor is bound to cause a lot of trouble. Your vehicle might get stuck in limp mode, and your engine could sustain heavy damage. Repairs could be extra costly, especially if the faulty sensor affects other parts. Save yourself a lot of time and money with a top-notch replacement from CarParts.com.
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Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
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What would cause a F350 to NOT have the power to move once you have put it in gear and try to move it just to have it die ?? But it will sit and idle with no issues!
Hi Billy,
What year is your F350 and what engine does it have (gas or diesel)? Are there any codes? Does it seem like the transmission isn't pulling or does it seem like more of an engine-related concern?
Hi Mia thanks for your response to my question!
It's a '90 F350 1 ton dually with a 460 ci Gas fuel injection engine ! The Transmission seems fine to me ,I'd just put a new clutch kit in it and you can sit and rev it up without issues and it will sit and idle almost like it loping ,and it sounds good to go until I put it in gear and try to take off and then it will spit and spider and dies ..not enough power to get it movin?? A guy said that there's a sensor on the trans .that probably got messed up because of the clutch being decent grated ..I've never seen a clutch in that condition ever before in my life??!
Hi Billy,
You're very welcome! For some reason, I assumed your truck was an automatic and a newer model. Did you have the problem before you put the clutch in or did the issue only pop up afterward? If the truck is stalling out immediately when you try to drive it, you likely have a fuel or spark delivery problem. Have you checked for fuel or spark delivery issues yet? Also, do you have access to an OBD1 scan tool that can pull live data on your truck? MAP sensor failures are common on this model truck and can cause stalling.