DIY Fix: How to Troubleshoot and Resolve Code 1518 on Your 2001 Subaru Outback

Are you a proud owner of a 2001 Subaru Outback and suddenly encountered a code 1518 on your car’s system? This can be a frustrating and confusing experience, especially if you don’t have a lot of experience with automotive issues. But don’t worry, with this step-by-step guide, you can troubleshoot and fix the problem yourself without having to go to a mechanic.

Understanding Code 1518 and Its Causes

First, let’s understand what code 1518 means. It is a diagnostic trouble code (DTC) that indicates there is an issue with the idle air control (IAC) valve in your car. The IAC valve is responsible for regulating air flow to the engine when the throttle is closed, ensuring that the engine maintains a stable idle speed. If there is an issue with this valve, it can cause rough idling, engine stalling, and decreased fuel efficiency.

There are several causes of a faulty IAC valve, including:

  • Clogged or dirty IAC valve
  • Failed IAC valve
  • Loose or damaged electrical connections to the IAC valve
  • Failed battery or alternator

Troubleshooting Code 1518

The first step in troubleshooting code 1518 is to inspect your car’s battery and alternator. A weak or dead battery can cause voltage fluctuations that can affect the performance of the IAC valve. You can determine if this is the issue by checking the voltage of your car’s battery with a voltmeter while the engine is running. The voltage should be between 13.5 and 14.5 volts. If the voltage is below this range, the issue may be with the alternator, and it should be checked by a mechanic.

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If the battery and alternator are functioning correctly, the next step is to inspect the IAC valve. To do this, you will need to remove the valve from the throttle body and clean it thoroughly with carburetor cleaner. Inspect the valve for any visible damage or wear, and if it appears to be in good condition, you can test it with a multimeter. The resistance of the valve should be between 6 and 13 ohms. If the resistance is outside of this range, the valve needs to be replaced.

If the valve appears to be in good condition and is functioning correctly, it’s time to inspect the electrical connections between the valve and the car’s computer system. Look for any loose or corroded connections, and repair or replace them as necessary. You can use a multimeter to check the continuity of the wiring between the valve and the computer.

Fixing Code 1518

Once you have identified the issue causing code 1518, it’s time to fix the problem. If the battery or alternator is the culprit, you may need to take your car to a mechanic to have them replaced. However, if the issue is with the IAC valve or its electrical connections, you can fix the problem yourself.

To remove the IAC valve, first, disconnect the electrical connector, vacuum hose, and throttle body hose attached to the valve. Then, use an adjustable wrench or pliers to remove the valve from the throttle body.

Clean the surfaces of the throttle body and IAC valve with carburetor cleaner and inspect again for any visible damage. If the valve needs to be replaced, you can purchase a new one from your local auto parts store or online retailer. Install the new valve onto the throttle body, reattach the electrical connector and hoses, and start the engine to test if the problem has been resolved.

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Q: Can a faulty IAC valve cause the engine to stall?
A: Yes, a faulty IAC valve can cause the engine to stall when the throttle is closed.

Q: How much does it cost to replace the IAC valve?
A: The cost of an IAC valve can vary depending on the make and model of your car and where you purchase the part. However, on average, an IAC valve can cost anywhere from $50 to $200.

Q: Do I need any special tools to replace the IAC valve?
A: No, you do not need any special tools to replace the IAC valve. A basic wrench or pliers should be sufficient.


Encountering code 1518 in your 2001 Subaru Outback can be a stressful experience, but with the right tools and knowledge, you can fix the problem yourself. By troubleshooting the issue, identifying the problem, and using our step-by-step guide, you can avoid a costly trip to the mechanic and have your car running smoothly once again. Remember to always be safe when working on your car and consult a mechanic if you are unsure about any aspect of the repair process.

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Billy Covington

With a passion for all things automotive, Billy is our go-to expert on Subaru performance upgrades and modifications. He's been featured in several car magazines and blogs, and his extensive knowledge and expertise make him a valuable member of our team. When he's not working on cars, he enjoys playing guitar and writing music.

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