Resetting the check engine light on a 2020 GMC Sierra isn’t just about clearing a warning—it’s about ensuring your truck is running properly. This guide walks you through safe, effective methods, from using an OBD2 scanner to driving cycles, so you can reset the light with confidence.
Key Takeaways
- Understand the cause first: Never reset the light without diagnosing the issue—ignoring problems can lead to costly repairs.
- Use an OBD2 scanner for best results: This tool reads error codes and safely clears the check engine light after repairs.
- Disconnecting the battery is a temporary fix: It may reset the light, but won’t clear stored codes and can affect other systems.
- Drive cycles help confirm repairs: After resetting, complete a driving cycle so the vehicle’s computer can verify everything is working.
- Check for pending codes: Even if the light is off, pending codes may remain—use a scanner to confirm full resolution.
- Keep records of repairs: Document what was fixed and when, especially if you plan to sell or inspect the vehicle.
- When to see a mechanic: If the light returns quickly or you’re unsure of the cause, professional diagnosis is recommended.
How to Reset Check Engine Light on 2020 GMC Sierra
So your 2020 GMC Sierra’s check engine light is on—again. Maybe it came on after filling up the gas tank, or perhaps it’s been glowing for days. Whatever the reason, that little orange icon on your dashboard can be stressful. But don’t panic. Resetting the check engine light is possible, and in many cases, you can do it yourself—safely and effectively.
This guide will walk you through everything you need to know about resetting the check engine light on your 2020 GMC Sierra. You’ll learn why the light comes on, how to diagnose the issue, and the best methods to reset it—whether you’re using a professional OBD2 scanner or just your vehicle’s built-in systems. We’ll also cover common mistakes to avoid, troubleshooting tips, and when it’s time to visit a mechanic.
By the end of this guide, you’ll feel confident handling the check engine light like a pro—no guesswork, no unnecessary trips to the shop, and no fear of hidden problems.
Why Is the Check Engine Light On?
Visual guide about How to Reset Check Engine Light on 2020 Gmc Sierra
Image source: thedrive.com
Before you think about resetting the light, it’s crucial to understand why it’s on in the first place. The check engine light—also known as the malfunction indicator lamp (MIL)—is part of your Sierra’s onboard diagnostics system (OBD2). It monitors engine performance, emissions, fuel system efficiency, and more.
When a sensor detects something out of the ordinary, the vehicle’s computer logs a trouble code and triggers the light. This could be something minor, like a loose gas cap, or something serious, like a failing catalytic converter.
Common causes for the check engine light on a 2020 GMC Sierra include:
- Loose or faulty gas cap: One of the most common reasons. A loose cap allows fuel vapors to escape, triggering an evaporative emissions code.
- Oxygen (O2) sensor failure: These sensors monitor exhaust gases and help regulate fuel mixture. A bad sensor reduces fuel efficiency and increases emissions.
- Mass airflow (MAF) sensor issues: This sensor measures how much air enters the engine. Dirt or malfunction can cause poor performance and rough idling.
- Catalytic converter problems: Over time, the converter can become clogged or damaged, leading to reduced performance and increased emissions.
- Spark plug or ignition coil failure: Misfires can damage the catalytic converter and reduce engine power.
- Evaporative emissions system leaks: Small leaks in the fuel vapor system can trigger codes like P0442 or P0455.
Ignoring the check engine light can lead to decreased fuel economy, increased emissions, and even engine damage. So, while resetting the light is possible, it should only be done after the underlying issue has been identified and fixed.
Tools You’ll Need to Reset the Check Engine Light
To reset the check engine light on your 2020 GMC Sierra, you’ll need a few basic tools. The good news? Most are affordable and easy to find.
OBD2 Scanner
This is the most reliable tool for diagnosing and resetting the check engine light. An OBD2 scanner plugs into the diagnostic port (usually under the dashboard) and reads trouble codes from your vehicle’s computer. Many scanners also allow you to clear codes and reset the light.
Look for a scanner that:
- Supports OBD2 protocols (all 2020 vehicles do)
- Can read and clear codes
- Displays code definitions (not just numbers)
- Has a user-friendly interface
Popular options include the BlueDriver Bluetooth Scanner, Autel MaxiCOM, or even basic models from brands like Innova or Foxwell. Prices range from $20 to $200, depending on features.
Owner’s Manual
Your 2020 GMC Sierra owner’s manual contains valuable information about the check engine light, including what it means and how to respond. It also shows the location of the OBD2 port and may include reset procedures.
Basic Hand Tools (Optional)
If you’re fixing a simple issue like a loose gas cap or replacing a sensor, you might need a wrench, screwdriver, or socket set. But for just resetting the light, these aren’t necessary.
Smartphone or Tablet (Optional)
Some Bluetooth OBD2 scanners connect to your phone via an app. Apps like Torque Pro (Android) or OBD Fusion (iOS/Android) let you view live data, read codes, and reset the light from your device.
Method 1: Using an OBD2 Scanner (Recommended)
The safest and most effective way to reset the check engine light is by using an OBD2 scanner. This method ensures you’re not just hiding a problem—you’re confirming it’s been fixed.
Step 1: Locate the OBD2 Port
In the 2020 GMC Sierra, the OBD2 port 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.
To find it:
- Sit in the driver’s seat and look under the steering column.
- You may need to crouch or use a flashlight.
- The port is often near the fuse box or brake pedal.
If you can’t find it, consult your owner’s manual—it will have a diagram.
Step 2: Plug in the OBD2 Scanner
Turn off the ignition, then plug the scanner into the OBD2 port. Make sure it’s fully inserted. Some scanners have a locking tab—press it gently to secure the connection.
Step 3: Turn on the Ignition
Turn the key to the “ON” position (but don’t start the engine). This powers up the vehicle’s computer and allows the scanner to communicate with it.
Step 4: Read the Trouble Codes
Follow the scanner’s instructions to read the codes. Most scanners will display something like “P0455” or “P0171.” These are diagnostic trouble codes (DTCs) that tell you what’s wrong.
Write down the codes. If your scanner shows definitions, great. If not, search online for “P0455 GMC Sierra” to understand the issue.
Step 5: Fix the Underlying Problem
Before resetting the light, fix the issue. For example:
- If the code is P0455 (large EVAP leak), check the gas cap. Tighten it or replace it if damaged.
- If it’s P0133 (O2 sensor slow response), you may need to replace the sensor.
- If it’s P0300 (random misfire), inspect spark plugs and ignition coils.
Never reset the light without addressing the cause. Doing so is like turning off a smoke alarm while the house is on fire.
Step 6: Clear the Codes
Once the problem is fixed, use the scanner to clear the codes. On most scanners, this is a simple button or menu option—like “Clear Codes” or “Erase DTCs.”
After clearing, the scanner may ask you to confirm. Select “Yes” or “OK.”
Step 7: Turn Off the Ignition and Unplug the Scanner
Turn the key back to “OFF,” then unplug the scanner. The check engine light should now be off.
Step 8: Start the Engine and Verify
Start your Sierra. The check engine light should remain off. If it comes back on, the problem wasn’t fully resolved—or a new issue has appeared.
Method 2: Disconnecting the Battery (Not Recommended)
Some people try to reset the check engine light by disconnecting the battery. While this can work, it’s not the best method—and here’s why.
How It Works
Disconnecting the battery cuts power to the vehicle’s computer, which can reset some systems and clear temporary codes. However, it doesn’t always clear all stored data, and it can cause other issues.
Step-by-Step: Disconnecting the Battery
- Turn off the engine and remove the key.
- Open the hood and locate the battery (usually on the driver’s side).
- Use a wrench to loosen the negative (-) terminal clamp.
- Remove the negative cable and tuck it away from the battery.
- Wait 15–30 minutes. This allows the computer to fully reset.
- Reconnect the negative cable and tighten the clamp.
- Start the engine and check if the light is off.
Why This Method Is Risky
- Doesn’t clear all codes: Some trouble codes are stored in non-volatile memory and won’t be erased.
- Resets other systems: You may lose radio presets, seat memory, or climate settings.
- Triggers new warnings: Disconnecting the battery can cause the “Service Theft Deterrent System” message or reset the oil life monitor.
- Doesn’t fix the problem: If the issue remains, the light will come back on—often within a few miles.
Only use this method if you don’t have access to an OBD2 scanner and need a temporary fix. But remember: it’s not a long-term solution.
Method 3: Drive Cycle Reset (Natural Reset)
Sometimes, the check engine light will turn off on its own—after you’ve fixed the problem and driven the vehicle through a specific pattern called a “drive cycle.”
A drive cycle is a series of driving conditions that allow the vehicle’s computer to run self-tests and confirm everything is working properly. Once all tests pass, the computer may automatically clear the codes and turn off the light.
How to Perform a Drive Cycle on a 2020 GMC Sierra
There’s no single universal drive cycle, but here’s a common pattern that works for many GM vehicles:
- Start the engine and let it idle for 2–3 minutes (cold start).
- Drive at 30–40 mph for about 5 minutes.
- Accelerate to 55–60 mph and maintain speed for 10 minutes.
- Decelerate to 20 mph without braking hard.
- Stop and idle for 2–3 minutes.
- Repeat the cycle 2–3 times over 30–60 minutes.
During this time, the computer tests systems like the oxygen sensors, catalytic converter, and evaporative emissions. If no faults are detected, it may clear the codes.
Important Notes
- This method only works if the problem has been fixed.
- The light may not turn off immediately—it can take several drive cycles.
- If the light stays on, use an OBD2 scanner to check for pending codes.
Troubleshooting Common Issues
Even after resetting the light, you might run into problems. Here’s how to handle them.
The Light Comes Back On
If the check engine light returns shortly after resetting, the issue wasn’t fully resolved. Use an OBD2 scanner to read the new codes. Common reasons include:
- Incorrect repair (e.g., replacing the wrong sensor)
- Intermittent fault (e.g., loose wiring)
- Multiple problems (e.g., bad O2 sensor and clogged catalytic converter)
Scanner Won’t Connect
If your OBD2 scanner won’t communicate with the vehicle:
- Check the OBD2 port for dirt or damage.
- Ensure the ignition is in the “ON” position.
- Try a different scanner or app.
- Verify the scanner is compatible with GM vehicles.
“Pending” Codes Remain
After clearing codes, you might see “pending” codes when you scan again. These are codes that haven’t yet triggered the light but are being monitored. Drive through a complete drive cycle to see if they clear.
Battery Disconnection Caused Other Issues
If you disconnected the battery and now have problems like:
- Radio asking for a code: Check your owner’s manual for the radio security code.
- Seat or mirror memory reset: Reprogram using the vehicle’s settings menu.
- “Service Theft Deterrent” message: This usually clears after driving for a few minutes.
When to See a Mechanic
While many check engine light issues can be handled at home, some require professional help. Visit a mechanic if:
- The light is flashing (indicates a severe misfire that can damage the catalytic converter).
- You’re unsure how to interpret the trouble codes.
- The problem involves internal engine components (e.g., timing chain, fuel injectors).
- The light keeps coming back despite repairs.
- You don’t have access to an OBD2 scanner or feel uncomfortable performing repairs.
A certified GM technician can perform advanced diagnostics, access manufacturer-specific codes, and ensure your Sierra is running safely.
Final Tips for Maintaining Your 2020 GMC Sierra
Preventing check engine light issues starts with regular maintenance. Here are some tips:
- Check the gas cap: After every fill-up, make sure it’s tight and the seal is intact.
- Use quality fuel: Stick to reputable gas stations to avoid contaminants.
- Follow the maintenance schedule: Replace spark plugs, air filters, and oxygen sensors as recommended.
- Listen for changes: Unusual noises, rough idling, or reduced power can signal trouble before the light comes on.
- Keep records: Document repairs and reset dates for future reference.
Conclusion
Resetting the check engine light on your 2020 GMC Sierra doesn’t have to be intimidating. With the right tools and knowledge, you can diagnose the issue, fix it properly, and clear the light with confidence. The best method is using an OBD2 scanner—it’s safe, accurate, and gives you full control.
Avoid quick fixes like disconnecting the battery unless absolutely necessary. And always remember: the light is there for a reason. Ignoring it can lead to bigger problems down the road.
By following this guide, you’ll not only reset the check engine light—you’ll also gain a better understanding of your truck’s health. Stay proactive, stay informed, and your Sierra will keep running strong for years to come.