This guide walks you through how to reset the check engine light on a 2015 GMC Sierra using simple methods like the OBD2 scanner, battery disconnect, or drive cycle. You’ll also learn when it’s safe to reset and when you should 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.
- Battery disconnect is a temporary fix: Disconnecting the battery may reset the light, but it can also erase important vehicle settings and won’t fix the root problem.
- Drive cycles can auto-reset the light: After repairs, driving under normal conditions for 50–100 miles may allow the vehicle’s computer to reset the light automatically.
- Check for pending codes: Even after a reset, the system may store pending codes. Use a scanner to verify the issue is truly resolved.
- Visit a mechanic if unsure: If the light returns or you’re uncomfortable performing diagnostics, seek professional help to avoid further damage.
- Keep records of repairs: Documenting fixes and resets helps with future troubleshooting and resale value.
How to Reset Check Engine Light on 2015 GMC Sierra
If you’ve noticed the check engine light glowing on your 2015 GMC Sierra’s dashboard, you’re not alone. This warning light is one of the most common—and sometimes most confusing—signals drivers encounter. While it might seem alarming, the check engine light is simply your vehicle’s way of saying, “Hey, something needs attention.” The good news? In many cases, you can reset it yourself—especially after you’ve fixed the underlying issue.
In this comprehensive guide, you’ll learn exactly how to reset the check engine light on a 2015 GMC Sierra. We’ll cover multiple methods, from using an OBD2 scanner to disconnecting the battery, and explain when each approach is appropriate. You’ll also discover how to interpret trouble codes, avoid common mistakes, and know when it’s time to call a professional. Whether you’re a DIY enthusiast or just want to save a trip to the mechanic, this guide has you covered.
By the end, you’ll feel confident diagnosing and resetting your check engine light—safely and effectively.
What Does the Check Engine Light Mean?
Before jumping into the reset process, it’s crucial to understand what the check engine light actually indicates. This amber or yellow light, often shaped like an engine or labeled “Check Engine,” is part of your Sierra’s onboard diagnostics system (OBD2). When it illuminates, it means the vehicle’s computer has detected a problem with the engine, emissions system, or related components.
Common causes include:
– A loose or faulty gas cap
– Oxygen (O2) sensor failure
– Catalytic converter issues
– Mass airflow (MAF) sensor problems
– Spark plug or ignition coil faults
– Exhaust gas recirculation (EGR) valve malfunctions
The light can come on steadily or flash. A steady light usually means a minor issue, while a flashing light indicates a severe problem—like engine misfiring—that could damage the catalytic converter if ignored.
Important: Never reset the check engine light without first identifying and addressing the root cause. Resetting it while a problem persists is like turning off a fire alarm while the house is still on fire. The light will likely return, and you risk further damage.
Tools You’ll Need
Before starting, gather the necessary tools. The method you choose will determine what you need:
- OBD2 Scanner: The best tool for reading and clearing trouble codes. Affordable models start around $20 and plug directly into your Sierra’s OBD2 port.
- Owner’s Manual: Helpful for locating the OBD2 port and understanding vehicle-specific procedures.
- Wrench or Socket Set: Needed if you plan to disconnect the battery.
- Safety Gloves and Glasses: Recommended for battery work.
- Notepad and Pen: To record trouble codes and repair notes.
Most 2015 GMC Sierra owners find an OBD2 scanner to be the most reliable and informative tool. It not only helps you reset the light but also tells you exactly what’s wrong—saving time and money.
Method 1: Using an OBD2 Scanner (Recommended)
The OBD2 scanner method is the most accurate and safest way to reset the check engine light. It allows you to read the trouble code, confirm the repair, and clear the light—all without guesswork.
Step 1: Locate the OBD2 Port
The OBD2 port in your 2015 GMC Sierra is typically located under the dashboard on the driver’s side. It’s a 16-pin connector, usually black or gray, and easy to spot once you know where to look.
To find it:
– Sit in the driver’s seat.
– Look down near the steering column.
– You should see the port just above the brake pedal, often behind a small panel or cover.
If you can’t find it, consult your owner’s manual—it will have a diagram showing the exact location.
Step 2: Plug in the OBD2 Scanner
Once you’ve located the port:
– Turn off the ignition.
– Plug the OBD2 scanner into the port firmly. Most scanners click into place.
– Turn the ignition to the “ON” position (but don’t start the engine). This powers the scanner and allows it to communicate with the vehicle’s computer.
Some scanners may require you to press a button to turn them on. Check your device’s instructions.
Step 3: Read the Trouble Code
With the scanner connected and powered:
– Follow the on-screen prompts to “Read Codes” or “Scan.”
– The scanner will retrieve one or more Diagnostic Trouble Codes (DTCs), such as P0420 (Catalytic Converter Efficiency Below Threshold) or P0171 (System Too Lean).
Write down the code(s). You can use free online resources like OBD-Codes.com to look up what each code means. This step is critical—it tells you exactly what needs fixing.
Step 4: Fix the Underlying Issue
Now that you know the problem, take steps to fix it. For example:
– If the code is P0455 (Large EVAP Leak), check and tighten your gas cap.
– If it’s P0133 (O2 Sensor Slow Response), you may need to replace the oxygen sensor.
Pro Tip: Some auto parts stores (like AutoZone or O’Reilly) offer free code reading. You can use their scanner to get the code, then buy the part and fix it yourself.
Step 5: Clear the Code and Reset the Light
After the repair is complete:
– Return to the scanner menu.
– Select “Clear Codes” or “Erase Codes.”
– Confirm the action when prompted.
The scanner will send a command to the vehicle’s computer to turn off the check engine light. You should see a message like “Codes Cleared” or “Reset Successful.”
Step 6: Verify the Reset
To ensure the light stays off:
– Turn the ignition off and wait 10–15 seconds.
– Turn it back on and check the dashboard. The check engine light should be off.
– If it’s still on, the problem may not be fully resolved, or there could be additional codes.
Drive the vehicle for 20–30 minutes under normal conditions. The computer will run self-tests. If no new codes appear, the reset was successful.
Method 2: Disconnecting the Battery
If you don’t have an OBD2 scanner, disconnecting the battery is a common alternative. However, this method has limitations and should be used with caution.
Step 1: Turn Off the Engine and Accessories
Make sure the vehicle is off. Turn off the radio, lights, and any other electrical accessories to avoid power surges.
Step 2: Locate the Battery
In the 2015 GMC Sierra, the battery is under the hood on the driver’s side. It’s a standard 12-volt lead-acid battery with positive (+) and negative (-) terminals.
Step 3: Disconnect the Negative Terminal
Using a wrench or socket:
– Loosen the nut on the negative (black) terminal.
– Carefully remove the cable and tuck it away from the battery so it doesn’t accidentally reconnect.
Safety Note: Always disconnect the negative terminal first to reduce the risk of short circuits.
Step 4: Wait 15–30 Minutes
Leave the battery disconnected for at least 15 minutes. This allows the vehicle’s computer (ECU) to fully reset and clear temporary memory, including the check engine light.
Some mechanics recommend waiting up to 30 minutes for a complete reset.
Step 5: Reconnect the Battery
After waiting:
– Reattach the negative cable and tighten the nut securely.
– Turn the ignition to “ON” and check the dashboard. The check engine light should be off.
Step 6: Drive and Monitor
Start the engine and take the truck for a short drive. The computer will begin running diagnostics. If the light returns, the original issue still exists.
Important Drawbacks:
– Disconnecting the battery resets more than just the check engine light. It can erase radio presets, clock settings, and adaptive transmission learning.
– It does not fix the underlying problem. If the issue persists, the light will come back.
– Some newer vehicles require a “relearn” procedure after battery disconnection, which may need professional tools.
Method 3: Drive Cycle Reset
In some cases, the check engine light will turn off on its own after the problem is fixed—no scanner or battery disconnect needed. This is called a “drive cycle reset.”
A drive cycle is a series of driving conditions that allow the vehicle’s computer to complete its self-tests. Once all tests pass, the computer may automatically clear the code and turn off the light.
How to Perform a Drive Cycle
While drive cycles vary by vehicle, a typical cycle for the 2015 GMC Sierra includes:
- Start the engine cold (hasn’t been run for at least 8 hours).
- Let it idle for 2–3 minutes.
- Drive at 30–40 mph for 3–5 minutes.
- Accelerate to 50–60 mph and maintain speed for 5–10 minutes.
- Decelerate slowly without braking hard.
- Stop and idle for 1–2 minutes.
- Repeat if necessary.
Complete this cycle 2–3 times over 50–100 miles of normal driving. Afterward, check if the light is off.
Note: Not all codes will clear automatically. Emissions-related codes (like P0420) often require a scanner reset, even after a successful drive cycle.
Troubleshooting Common Issues
Even after resetting the light, you might encounter problems. Here’s how to handle them:
The Light Comes Back On
If the check engine light returns shortly after a reset, the issue wasn’t fully resolved. Possible reasons:
– The repair was incomplete (e.g., gas cap tightened but still faulty).
– A secondary problem exists.
– The sensor needs time to recalibrate.
Use an OBD2 scanner to check for new or pending codes. Pending codes are stored but haven’t triggered the light yet—they can give you early warning.
Scanner Won’t Connect
If your OBD2 scanner fails to communicate:
– Ensure the ignition is on (but engine off).
– Check that the scanner is fully plugged in.
– Try a different scanner or visit an auto parts store for a free scan.
– Inspect the OBD2 port for dirt or damage.
Battery Disconnect Didn’t Work
If disconnecting the battery didn’t reset the light:
– The ECU may have non-volatile memory that retains codes.
– The issue may be too severe for a simple reset.
– Try combining the battery disconnect with a drive cycle.
Radio or Settings Reset After Battery Disconnect
This is normal. To restore settings:
– Re-enter radio presets.
– Reset the clock.
– Some vehicles may need a “steering angle sensor” or “transmission relearn” procedure—consult a mechanic if unsure.
When to See a Mechanic
While many check engine light issues can be handled at home, some situations require professional help:
- The light is flashing—this indicates a serious engine misfire that can damage the catalytic converter.
- You’re unable to read or interpret the trouble code.
- The problem involves complex components like the transmission, fuel injectors, or engine internals.
- The light keeps returning despite multiple resets and repairs.
- You notice performance issues like rough idling, stalling, or reduced fuel economy.
A certified mechanic has advanced diagnostic tools and expertise to pinpoint and fix complex issues. Don’t hesitate to seek help if you’re unsure.
Preventing Future Check Engine Light Issues
An ounce of prevention is worth a pound of cure. Follow these tips to reduce the chances of the check engine light coming on:
- Replace the gas cap if it’s loose or damaged. A faulty cap is one of the most common causes.
- Use quality fuel and oil. Contaminated or low-grade fuel can trigger sensor errors.
- Follow the maintenance schedule. Replace spark plugs, air filters, and O2 sensors as recommended.
- Address warning lights promptly. Ignoring small issues can lead to bigger, costlier problems.
- Keep the engine clean. Dirt and debris can affect sensor performance.
Regular maintenance not only prevents check engine lights but also extends the life of your Sierra.
Conclusion
Resetting the check engine light on your 2015 GMC Sierra doesn’t have to be intimidating. With the right tools and knowledge, you can safely and effectively clear the light—especially after addressing the root cause. The OBD2 scanner method is the most reliable, offering precise diagnostics and a clean reset. Battery disconnection and drive cycles are useful alternatives but come with limitations.
Remember: the check engine light is your vehicle’s way of communicating. Don’t silence it without understanding the message. Always diagnose the problem first, fix it properly, and then reset the light. By doing so, you’ll keep your Sierra running smoothly, avoid costly repairs, and drive with confidence.
Whether you’re a seasoned DIYer or a first-time troubleshooter, this guide equips you with everything you need to handle the check engine light like a pro.