Mastering the Art of Subaru Fuel Trim Clearing: DIY Guide for Optimal Car Performance

As a Subaru car owner, you understand the importance of your vehicle’s performance and the role fuel trims play in achieving optimal performance. Understanding fuel trims can help you diagnose and fix performance issues quickly, allowing you to enjoy a smooth and efficient ride. In this article, we will cover the basics of fuel trims, the symptoms of a faulty fuel trim, and a step-by-step guide to clear fuel trims in your Subaru car.

What are fuel trims?

Fuel trims are designed to monitor and adjust the air/fuel ratio in your car’s engine. The computer-controlled system determines the correct air/fuel ratio based on a variety of inputs, including engine load, temperature, and air pressure. If the ratio is too rich or lean, the fuel trims will adjust the ratio to ensure optimal engine performance.

Symptoms of a Faulty Fuel Trim

A common symptom of a faulty fuel trim is poor fuel economy. If your fuel trim is consistently too rich, you may experience reduced gas mileage, meaning you may need to fuel up more often than before. In contrast, a fuel trim that is too lean can cause your car to stall or have reduced power during acceleration.

Another common symptom of faulty fuel trims is the engine warning light on your dashboard illuminating. This warning implies that there is a problem with the engine, and you should have it checked out as soon as possible.

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Step-by-step guide to Clearing Fuel Trims in your Subaru Car

Tools Required

  • OBD2 Scanner
  • Socket Wrench Set
  • Safety Glasses

Step-by-Step Guide

  1. Before starting any DIY auto maintenance task, always ensure that the engine is off and has cooled down. Then, locate the OBD2 port in your Subaru. This port is usually located to the left or right of the pedal area. Plug your OBD2 scanner into the port.

  2. Turn on your ignition key to the "ON" position, but do not start the engine. Your scanner will communicate with your Subaru’s computer system, and you will receive a series of fault codes. Look for fuel trim codes with the letters "LTFT" and "STFT." These codes provide information on your fuel trims.

  3. If your fuel trim codes are too lean or too rich, you can reset them using your scanner. Press the corresponding button on your scanner to clear the codes. Doing this resets your fuel trims to their default settings.

  4. Once you have cleared the codes, turn off the ignition key, disconnect your scanner, and close the OBD2 port door.

  5. Restart your Subaru and observe the engine’s performance. If the fuel trim codes have returned to normal, your car’s performance has likely improved. However, if the performance issue persists, there may be underlying problems that will require further investigation.

Potential Risks or Challenges

Clearing fuel trims on your car can be a straightforward process. However, if done incorrectly, it may cause further issues in your engine’s performance. Moreover, when working on any automotive task, safety should be your top priority. Be sure to wear safety glasses to protect your eyes from debris or extraneous materials.

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Clearing fuel trims in your Subaru is an essential DIY task for optimizing your car’s performance. By following the step-by-step guide provided in this article, you can quickly and efficiently diagnose and fix fuel trim issues in your car. Always remember that safety should come first before working on any auto maintenance task. With this knowledge, you can save both time and money while ensuring you get the best performance from your Subaru for years to come.


  1. What causes a faulty fuel trim in my Subaru car?
    The most common causes of a faulty fuel trim may include a vacuum leak, malfunctioning oxygen sensors, clogged injectors, or a damaged catalytic converter.

  2. How often should I clear my fuel trims in my Subaru car?
    There is no specific time frame to clear fuel trims in your car. However, if you experience any of the above symptoms we mentioned, it’s best to clear the trims and check the performance of your engine.

  3. Can I clear fuel trims without using an OBD2 scanner?
    No, clearing fuel trims on your car requires an OBD2 scanner that is compatible with Subaru vehicles.

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Alton Brobst

As a longtime Subaru enthusiast, Alton brings a wealth of knowledge and experience to our blog. From his early days of tinkering with engines to his current role as a certified Subaru technician, Alton has seen it all when it comes to Subarus. When he's not working on cars, he enjoys hiking and exploring the great outdoors.

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