This guide walks you through how to reset the check engine light on a 2015 Subaru Forester using simple methods like driving cycles, battery disconnection, or an OBD2 scanner. You’ll also learn when it’s safe to reset and when to see a mechanic.
Key Takeaways
- Understand the cause first: Never reset the check engine light without diagnosing the underlying issue. Ignoring problems can lead to costly repairs or unsafe driving conditions.
- Use an OBD2 scanner for accuracy: This is the most reliable and recommended method. It reads the trouble code, confirms the fix, and safely clears the light.
- Driving cycles can auto-reset the light: After fixing the issue, completing a specific driving pattern may turn off the light without tools.
- Battery disconnection is a temporary fix: While it can reset the light, it also erases ECU memory and may not work if the problem persists.
- Check gas cap regularly: A loose or damaged gas cap is a common cause of the light coming on and is easily fixed.
- Resetting doesn’t fix the problem: The light will return if the issue isn’t resolved. Always verify repairs before clearing codes.
- Visit a mechanic if unsure: If you can’t identify or fix the problem, professional diagnosis ensures safety and prevents further damage.
How to Reset Check Engine Light on 2015 Subaru Forester
If you’ve recently fixed an issue with your 2015 Subaru Forester and the check engine light is still on, you’re not alone. Many drivers face this frustrating situation. The good news? Resetting the check engine light is often simple—but it should never be done without understanding why the light came on in the first place.
In this complete guide, you’ll learn how to reset the check engine light on a 2015 Subaru Forester using safe, effective methods. We’ll cover everything from using an OBD2 scanner to driving cycles and even battery disconnection. You’ll also learn when it’s safe to reset the light and when it’s time to visit a professional.
By the end of this guide, you’ll know exactly what steps to take, what tools you need, and how to avoid common mistakes. Whether you’re a DIY enthusiast or just want to save a trip to the mechanic, this guide has you covered.
Why the Check Engine Light Comes On
Visual guide about How to Reset Check Engine Light on 2015 Subaru Forester
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Before you reset the light, it’s important to understand why it turned on in the first place. The check engine light—also known as the malfunction indicator lamp (MIL)—is part of your vehicle’s onboard diagnostics system (OBD2). It alerts you when the engine control unit (ECU) detects a problem that could affect emissions, performance, or fuel efficiency.
On a 2015 Subaru Forester, common causes include:
- A loose or faulty gas cap
- Oxygen (O2) sensor failure
- Mass airflow (MAF) sensor issues
- Catalytic converter problems
- Spark plug or ignition coil failure
- Exhaust gas recirculation (EGR) valve malfunction
- Evaporative emissions system leaks
Some of these issues are minor and easy to fix—like tightening the gas cap. Others may require professional attention. That’s why diagnosing the problem is the first and most important step.
Can You Just Reset the Light Without Fixing the Problem?
Short answer: No.
Resetting the check engine light without addressing the root cause is like turning off a fire alarm while the house is still burning. The light will likely come back on—and the problem could get worse.
For example, if the light is on because of a failing oxygen sensor, resetting it won’t fix the sensor. Your car will continue running inefficiently, possibly increasing emissions and reducing fuel economy. In some cases, it could even damage the catalytic converter, which is expensive to replace.
So, before you reset the light, make sure the issue has been resolved. If you’re not sure what caused the light, use an OBD2 scanner to read the trouble code. This will tell you exactly what system or component is malfunctioning.
Method 1: Use an OBD2 Scanner (Recommended)
The best and most reliable way to reset the check engine light on your 2015 Subaru Forester is by using an OBD2 scanner. This tool connects to your car’s diagnostic port and communicates with the ECU to read and clear trouble codes.
What You’ll Need
- An OBD2 scanner (basic models start around $20)
- Your 2015 Subaru Forester
- Access to the OBD2 port (usually under the dashboard)
Step-by-Step Instructions
Step 1: Locate the OBD2 Port
The OBD2 port in the 2015 Subaru Forester is typically located under the dashboard on the driver’s side. It’s a 16-pin connector, usually black or gray, and may be covered by a small flap. You don’t need any tools to access it—just reach under the steering column and look for the port.
Step 2: Turn the Ignition to “On”
Insert your key and turn the ignition to the “On” position. Do not start the engine—just turn it so that the dashboard lights up. This powers the ECU and allows the scanner to communicate with the vehicle.
Step 3: Plug in the OBD2 Scanner
Connect the OBD2 scanner to the port. Make sure it’s firmly seated. Most scanners will power on automatically when plugged in.
Step 4: Read the Trouble Codes
Follow the scanner’s instructions to read the diagnostic trouble codes (DTCs). These codes will tell you what system is malfunctioning. For example:
- P0455: Large evaporative emissions leak (often a loose gas cap)
- P0133: O2 sensor circuit slow response
- P0301: Cylinder 1 misfire detected
Write down the code(s) so you can research the issue or show them to a mechanic.
Step 5: Fix the Problem
Based on the code, take the necessary steps to fix the issue. For example:
- If the code is P0455, check and tighten the gas cap. Replace it if it’s cracked or worn.
- If it’s a misfire code, inspect spark plugs and ignition coils.
- If it’s an O2 sensor code, consider replacing the sensor.
Step 6: Clear the Codes
Once the problem is fixed, return to the OBD2 scanner and select the option to “Clear Codes” or “Erase DTCs.” The scanner will send a command to the ECU to reset the check engine light.
Step 7: Turn Off the Ignition and Restart
Turn the ignition off, wait 10–15 seconds, then start the engine. The check engine light should be off. If it comes back on, the problem may not be fully resolved, or a new issue has occurred.
Tips for Using an OBD2 Scanner
- Choose a scanner with a clear display and easy navigation. Bluetooth models that connect to your smartphone are convenient.
- Some scanners offer live data, which can help you monitor sensor performance in real time.
- Always clear codes after repairs—don’t just read them and ignore them.
- If the light returns after clearing, don’t panic. It may take a few drive cycles for the system to confirm the fix.
Method 2: Complete a Drive Cycle
If you’ve fixed the issue but don’t have an OBD2 scanner, your 2015 Subaru Forester may reset the check engine light automatically after completing a specific driving pattern known as a “drive cycle.”
A drive cycle is a series of driving conditions that allow the ECU to test various emissions systems. Once all tests pass, the check engine light will turn off.
How to Perform a Drive Cycle on a 2015 Subaru Forester
Follow these steps carefully. The drive cycle must be completed in one continuous trip without turning off the engine.
Step 1: Cold Start
Start the engine when it’s cold—ideally, after the car has been sitting for at least 8 hours. Let it idle for 2–3 minutes to warm up slightly.
Step 2: City Driving
Drive at speeds between 25–35 mph for about 3–5 minutes. Make several stops and accelerations to simulate normal city driving.
Step 3: Highway Driving
Accelerate to 55–65 mph and maintain that speed for 5–10 minutes. This allows the catalytic converter and oxygen sensors to reach operating temperature.
Step 4: Deceleration
Slow down gradually without braking hard. Let the car coast in gear to allow the EGR system to be tested.
Step 5: Stop and Idle
Come to a complete stop and let the engine idle for 2–3 minutes.
Step 6: Repeat if Necessary
If the light doesn’t turn off after one cycle, repeat the process. Some systems require multiple drive cycles to complete their tests.
Important Notes
- The drive cycle may take 30–60 minutes to complete.
- Do not turn off the engine during the cycle.
- If the light was on due to a serious issue (like a misfire), it may not reset automatically.
- This method works best for minor issues like a loose gas cap or minor sensor glitches.
Method 3: Disconnect the Battery
Another way to reset the check engine light is by disconnecting the car battery. This cuts power to the ECU, forcing it to reset. However, this method has drawbacks and should be used with caution.
How to Disconnect the Battery
Step 1: Turn Off the Engine and Remove the Key
Make sure the car is completely off and the key is out of the ignition.
Step 2: Locate the Battery
In the 2015 Subaru Forester, the battery is in the engine bay on the driver’s side.
Step 3: Disconnect the Negative Terminal
Use a wrench to loosen the nut on the negative (black) battery terminal. Remove the cable and secure it away from the battery post so it doesn’t accidentally reconnect.
Step 4: Wait 15–30 Minutes
Leave the battery disconnected for at least 15 minutes. This allows the ECU to fully reset. Some recommend up to 30 minutes for a complete reset.
Step 5: Reconnect the Battery
Reattach the negative cable and tighten the nut securely.
Step 6: Start the Engine
Turn the ignition on and start the car. The check engine light should be off—at least temporarily.
Drawbacks of Battery Disconnection
- Erases ECU memory: This includes learned driving patterns, radio presets, and climate control settings. Your car may run rough for a few miles until the ECU relearns.
- May not work: If the problem still exists, the light will come back on after a few drive cycles.
- Resets other systems: Some features like the clock, seat memory, or navigation system may need to be reset.
When to Use This Method
Only use battery disconnection if you don’t have an OBD2 scanner and have already fixed the issue. It’s a last-resort method, not a recommended one.
Troubleshooting Common Issues
Even after following the steps above, you might run into problems. Here’s how to handle common issues.
The Light Comes Back On After Reset
If the check engine light returns after you’ve reset it, the original problem likely wasn’t fully fixed. For example:
- A new gas cap may not seal properly if the filler neck is damaged.
- An O2 sensor may need replacement, not just cleaning.
- A misfire could be due to a bad fuel injector, not just a spark plug.
Use an OBD2 scanner to read the code again. Compare it to the original code—if it’s the same, the fix wasn’t complete.
The Light Won’t Turn Off
If the light stays on even after a drive cycle or battery reset, there may be an ongoing issue. Possible causes:
- A faulty sensor that needs replacement
- An electrical problem, like a short circuit
- A software glitch in the ECU
In this case, visit a Subaru dealership or trusted mechanic for a professional diagnosis.
The Car Runs Rough After Reset
If your Forester feels sluggish or stalls after a reset, the ECU may need time to relearn driving patterns. Drive normally for 50–100 miles. If problems persist, have the vehicle inspected.
When to See a Mechanic
While many check engine light issues can be resolved at home, some require professional help. Visit a mechanic if:
- The light is flashing (this indicates a severe misfire that can damage the catalytic converter)
- You’re unable to read or interpret the trouble code
- The problem involves the transmission, fuel system, or emissions control
- You’ve tried resetting the light multiple times and it keeps returning
- You’re not comfortable performing repairs yourself
A certified Subaru technician has access to advanced diagnostic tools and factory service information, ensuring accurate repairs.
Preventing Future Check Engine Light Issues
The best way to avoid dealing with the check engine light is to prevent problems before they start. Here are some tips:
- Check the gas cap regularly: Make sure it’s tight after every fill-up. Replace it every 5 years or if it shows signs of wear.
- Follow the maintenance schedule: Replace spark plugs, air filters, and oxygen sensors as recommended in your owner’s manual.
- Use quality fuel: Stick to reputable gas stations to avoid contaminated fuel.
- Address warning signs early: If you notice rough idling, poor fuel economy, or hesitation, get it checked out before the light comes on.
- Keep the engine clean: Regularly inspect the engine bay for leaks, loose hoses, or damaged wiring.
Final Thoughts
Resetting the check engine light on your 2015 Subaru Forester doesn’t have to be complicated. With the right tools and knowledge, you can safely clear the light after fixing the underlying issue. The OBD2 scanner method is the most reliable, while drive cycles and battery disconnection can work in a pinch.
Remember: resetting the light is not a fix. Always diagnose and repair the problem first. Ignoring the cause can lead to bigger, more expensive issues down the road.
By following this guide, you’ll save time, money, and stress. Keep your Forester running smoothly—and keep that check engine light off for good.