The Ultimate Guide: How to Test and Troubleshoot Your Subaru Throttle Position Sensor

If you own a Subaru vehicle, it’s important to keep its various components maintained and in good condition for optimal performance. One crucial component that plays a significant role in the functioning of your Subaru is the throttle position sensor (TPS).

In this guide, we will be providing step-by-step instructions on how to test and troubleshoot your Subaru’s TPS to ensure it’s functioning correctly. We will also be covering what a TPS is, its function in a vehicle, its signs and symptoms of failure, and the tools required for testing and troubleshooting.

Understanding the Throttle Position Sensor (TPS)

Before we dive into how to test and troubleshoot your Subaru’s TPS, let’s first understand what it is and its function in a vehicle.

A TPS is a sensor that reads the position of the throttle valve. It sends a signal to the vehicle’s engine control module (ECM), which then adjusts the engine’s fuel injection and ignition timing based on the position of the throttle. This means that the TPS plays a crucial role in regulating the engine’s performance and fuel efficiency.

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Signs and Symptoms of a Faulty Throttle Position Sensor

One of the tell-tale signs of a faulty TPS is a decrease in engine performance or fuel economy. Here are some common symptoms of a faulty TPS:

  • Poor or rough idling
  • Difficulty starting the car
  • Stalling or jerking while driving
  • Sudden changes in acceleration speed
  • Non-responsive acceleration

If you are experiencing any of these symptoms, it’s essential to test your Subaru’s TPS to identify if it’s the cause of the problem.

Tools and Equipment Required for Testing the Sensor

To test your Subaru’s TPS, you’ll need the following tools:

  • Digital multimeter
  • Back-probing pins
  • Safety glasses
  • Clean rags or towels

It’s crucial to wear safety glasses when working on your vehicle to protect your eyes from any possible debris or loose parts.

Step-by-Step Instructions on How to Test the Sensor

Now that you have all the necessary tools let’s begin with the testing process. Below are the steps to follow:

Step 1: Locate the TPS

The TPS is usually located on the throttle body of your Subaru. Consult your vehicle owner’s manual to locate your car’s TPS.

Step 2: Disconnect the Electrical Connector

Using your back-probing pins, gently disconnect the electrical connector to access the TPS.

Step 3: Connect the Multimeter

Set your digital multimeter to DC voltage and connect it to the TPS. Use one of the back-probing pins to connect the multimeter’s positive probe to the signal wire, and the negative probe to the ground wire.

Step 4: Check the Voltage Values

With your multimeter properly connected, turn the ignition key to the "on" position without starting the engine. Check the voltage reading on your multimeter; it should be around 0.5 volts.

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Next, slowly move the throttle valve to the full open position and then back to the closed position. As you do this, watch the voltage reading on your multimeter. The voltage should increase smoothly as you open the throttle and decrease smoothly as you close it. If the voltage reading fails to change or read numbers out of the normal range, then your TPS is faulty and in need of replacing.

Troubleshooting Common Issues

If your TPS is reading incorrectly, you can follow these steps to troubleshoot the issue:

  • Check for loose electrical connections
  • Check for damaged or corroded wires
  • Check that the TPS is properly mounted
  • Clean the throttle body and the TPS using a throttle body cleaner and a clean rag

If the above troubleshooting steps fail to resolve the issue, it may be time to replace your Subaru’s TPS.

How to Fix or Replace a Faulty Throttle Position Sensor

To replace your Subaru’s TPS, follow these steps:

  1. Disconnect the electrical connector and unscrew the old TPS from the throttle body.
  2. Replace the old TPS with the new one and reconnect the electrical connector.
  3. Turn on your engine to ensure the TPS is working correctly after replacing it.


How do I know if my Subaru’s TPS is faulty?

If you are experiencing poor idling, difficulty starting your car, stalling or jerking while driving, sudden changes in acceleration speed, or non-responsive acceleration, your TPS may be faulty.

How often should I test my Subaru’s TPS?

It’s recommended that you test your Subaru’s TPS every time you perform a tune-up to ensure it’s functioning correctly.

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Can I continue to drive my car with a faulty TPS?

It’s highly discouraged to drive your car with a faulty TPS as it can cause further damage to your vehicle’s engine and decrease its fuel efficiency.

In conclusion, as a Subaru enthusiast, it’s crucial to maintain your vehicle’s various components, including the throttle position sensor. Following the above testing and troubleshooting guide, you’ll be able to identify if your TPS is faulty, fix any issues or even replace it if necessary.

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Davis Bellew

As a Subaru owner and enthusiast, Davis has a deep understanding of the needs and concerns of Subaru drivers. He specializes in writing informative and engaging content about Subaru maintenance and repair, and his articles are always well-researched and easy to understand. When he's not writing, he enjoys hiking and photography.

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