2009 Subaru Legacy Has A Check Engine Light

Troubleshooting the Check Engine Light in Your 2009 Subaru Legacy: Common Causes and Solutions

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Reviewed by
Devin Cabugcal
Written by RepairPal Car Genius
Updated January 14, 2025
0%
40% chance it's the
Emissions System
0%
60% chance it's
Something else
The most common reasons a 2009 Subaru Legacy has a check engine light are an emissions system component, a sensor, or a catalytic converter.
  • Emissions System: A faulty emissions system component, such as an oxygen sensor or EGR valve, can lead to increased emissions and trigger the check engine light.
Proper diagnosis will determine the exact cause of your symptom, saving you money on unnecessary repairs. The diagnostic experts at RepairPal Certified shops have the right tools and experience to solve any symptom.

How much does it cost to fix a 2009 Subaru Legacy has a check engine light?

Common Repairs

The total repair cost will vary based on the condition of your vehicle and the number of repairs needed to fix your symptom. Proper diagnosis will save you money by finding the exact repairs needed to fix your car right the first time.

Any time there is an emissions fault the check engine light will be displayed. The purpose of the check engine light is to inform the driver that an emission related fault has been found, and that there are on-board diagnostic (OBD) trouble codes stored in the powertrain or engine control module. Additionally, since the emissions systems are so intertwined into engine control and transmission control systems, symptoms may include nearly any sort of drivability concerns. This may include harsh shifting, failure to shift, hesitation on acceleration, jerking, engine failure to start or run, loss of power, or any number of other drivability issues.

Due to the nature of electrical systems on modern vehicles, the range of problems these can cause are nearly limitless. However, there is a way to categorize them in two ways. Permanent and intermittent problems. Permanent problems appear and remain. This may be the vehicle will not start, the radio does not work, or the door chime will not turn off among many, many others. These problems are more straight-forward to diagnose since they present themselves at all time. This means there will always be a fault to find. Intermittent electrical problems, however, can be difficult or impossible to locate, since they appear then disappear without warning. The best case scenario for an intermittent issue is when replicating the problem is easily accomplished and understood. This allows a technician to make an issue semi-permanent, allowing them to find the fault. Other issues that come and go without warning and cannot be replicated on demand must occur when the technician is servicing the vehicle, otherwise there is no problem to correct. It is most important to understand that electrical system faults always require inspection, and can include the vehicle working in any manner, or not working at all.

Like we noted in the last section, general diagnosis symptoms are the most vague of the bunch. There are several diagnostic spectrums, electrical diagnosis, drivability diagnostics, engine diagnostics, transmission diagnostics, and the list could continue for about 5 or 10 more spectrums of diagnostics. The most important take-away here, is that general diagnostics are diagnostics that have no other spectrum in which they fit, or the problem is unknown. This means that any vehicle left outside of a repair facility with the keys and an authorization to perform diagnosis will be diagnosed under the general diagnosis spectrum.

When the Check Engine Light comes on, you may experience engine performance issues such as poor acceleration, rough idling, or an engine that won't start. In some cases, no abnormal symptoms will be experienced. Other systems like the transmission or ABS can cause the Check Engine Light to illuminate and lights for those systems can come on at the same time. Similar lights may say "Check Engine Soon", "Malfunction Indicator Light" or just "Check". In rare case the engine can overheat.

What are the initial diagnostic steps to take for a check engine light on a 2009 Subaru Legacy?

When faced with a check engine light on your 2009 Subaru Legacy, it's essential to adopt a systematic diagnostic approach that begins with the simplest solutions before progressing to more complex diagnostics. Start by checking the basics, such as ensuring that the gas cap is securely tightened, as a loose cap is a common and easily fixable cause of the warning light. Next, utilize the vehicle's dashboard display to access Diagnostic Trouble Codes (DTCs) without needing a scan tool. This method involves a series of steps that allow you to cycle through the modules and view any error codes directly on the dashboard, providing immediate insight into potential issues. If you prefer a more detailed analysis, consider using an OBD-II scanner, which connects to the vehicle's OBD-II port and offers comprehensive trouble code readings along with the ability to reset them if necessary. Pay attention to the severity of the check engine light; a steady light may indicate a minor issue, while a flashing light signals a serious problem that requires urgent attention. By following this structured approach, you can effectively diagnose the issue and determine the appropriate next steps, whether that involves a simple fix or seeking professional assistance.

What are the common problems that could cause the check engine light to illuminate in a 2009 Subaru Legacy?

When addressing the check engine light in a 2009 Subaru Legacy, it's crucial to recognize the common problems that may be causing this warning. A loose or missing gas cap is often the simplest issue, leading to fuel vapor leaks that can impact fuel efficiency and emissions. Ignition system faults, such as worn spark plugs or defective ignition coils, can also trigger the light by causing engine misfires. Additionally, a malfunctioning oxygen sensor is a significant concern, as it regulates the air-fuel mixture; its failure can result in poor engine performance. The mass air flow sensor is another critical component that, if dirty or faulty, can disrupt the engine's air-fuel balance. Emissions control issues, particularly with the catalytic converter, are also common culprits, as they play a vital role in minimizing harmful emissions. Other potential triggers include problems within the transmission or fuel system, as well as engine misfires that require prompt attention to avoid further damage. Lastly, a faulty coolant temperature sensor or issues with the EVAP system can contribute to the check engine light illuminating. By understanding these potential issues, you can effectively diagnose and resolve the check engine light, ensuring your Subaru Legacy operates smoothly.

How urgent is it to address the check engine light in a 2009 Subaru Legacy?

When it comes to the check engine light in your 2009 Subaru Legacy, understanding the urgency of the situation is crucial for both safety and vehicle longevity. If the light is steady, it often points to minor issues like a loose gas cap or a dirty mass airflow sensor, which, while still needing attention, can typically wait for a scheduled maintenance check. However, if the light is blinking, this signals a serious problem, such as an engine misfire, which can lead to severe damage if not addressed immediately. In such cases, it’s advisable to refrain from driving the vehicle and seek professional help to avoid costly repairs down the line. Additionally, if you notice performance issues like a decrease in power or the vehicle entering "limp-mode," these symptoms further underscore the need for prompt action. Ignoring these warning signs can lead to significant damage, including potential harm to the catalytic converter. Therefore, whether the light is steady or blinking, it’s essential to diagnose the issue as soon as possible to ensure your Subaru remains safe and reliable on the road.

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