Resetting the check engine light on a 2015 Fiat doesn’t have to be complicated. This guide walks you through safe, proven methods—from using an OBD2 scanner to driving cycles—so you can clear the light and ensure your car runs smoothly.
Key Takeaways
- Understand the cause first: Never reset the light without diagnosing the underlying issue—doing so may mask serious problems.
- Use an OBD2 scanner for accuracy: This is the most reliable way to read codes and reset the light on a 2015 Fiat.
- Battery disconnection is a temporary fix: While it may reset the light, it also erases important vehicle data and may not work long-term.
- Complete a drive cycle after reset: Your Fiat needs to run through specific conditions for the system to recheck emissions and confirm repairs.
- Check for pending codes: Even if the light is off, unresolved issues may still be stored in the system.
- Use quality fuel and maintenance: Prevent future triggers by using the right fuel, changing oil regularly, and inspecting spark plugs.
- Seek professional help if needed: Persistent lights or complex codes may require a certified mechanic’s expertise.
How to Reset Check Engine Light on 2015 Fiat
If you’ve noticed the dreaded check engine light glowing on your 2015 Fiat dashboard, you’re not alone. This warning light can appear for dozens of reasons—from a loose gas cap to a failing oxygen sensor. While it’s natural to want to turn it off quickly, simply resetting the light without addressing the root cause can lead to bigger problems down the road.
In this comprehensive guide, you’ll learn how to safely and effectively reset the check engine light on your 2015 Fiat. We’ll walk you through multiple methods—from using an OBD2 scanner to disconnecting the battery—and explain when each is appropriate. You’ll also discover how to perform a proper drive cycle, interpret diagnostic trouble codes, and prevent future check engine light activations.
Whether you’re a DIY enthusiast or just want to understand what’s happening under the hood, this guide will give you the knowledge and confidence to handle the situation like a pro.
Why the Check Engine Light Comes On
Before jumping into resetting the light, it’s crucial 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 Fiat’s onboard diagnostic system (OBD2). This system constantly monitors engine performance, emissions, and various sensors.
When something goes out of spec, the system logs a diagnostic trouble code (DTC) and illuminates the check engine light. Common causes on a 2015 Fiat include:
- Loose or faulty gas cap: A simple but frequent culprit. If the cap isn’t sealed properly, fuel vapors can escape, triggering the light.
- Oxygen (O2) sensor failure: These sensors monitor exhaust gases and help regulate fuel mixture. A faulty sensor can reduce fuel efficiency and increase emissions.
- Spark plug or ignition coil issues: Misfires can cause rough idling, poor acceleration, and trigger the light.
- Catalytic converter problems: Often a result of long-term neglect, a failing converter can lead to reduced performance and increased emissions.
- Mass airflow (MAF) sensor malfunction: This sensor measures how much air enters the engine. If it’s dirty or broken, your Fiat may run rich or lean.
- Evaporative emissions system leaks: Small leaks in the EVAP system can trigger the light even if they’re hard to detect.
Ignoring the light can lead to decreased fuel economy, engine damage, or even failure to pass emissions tests. That’s why diagnosing the issue before resetting the light is essential.
Method 1: Use an OBD2 Scanner (Recommended)
The most accurate and reliable way to reset the check engine light on a 2015 Fiat is by using an OBD2 scanner. This tool plugs into your car’s diagnostic port and communicates directly with the engine control unit (ECU).
Step 1: Locate the OBD2 Port
In the 2015 Fiat 500, the OBD2 port is typically located under the dashboard on the driver’s side. You’ll find it near the steering column, often behind a small panel or cover. It’s a 16-pin connector that looks like a trapezoid.
To access it:
- Sit in the driver’s seat and look down near your knees.
- Feel around for a small rectangular port.
- If it’s covered, gently remove the plastic cover by hand or with a flathead screwdriver.
Step 2: Plug in the OBD2 Scanner
Turn off the ignition before connecting the scanner. Once the port is accessible:
- Plug the OBD2 scanner into the port firmly.
- Turn the ignition to the “ON” position (do not start the engine yet).
- Wait for the scanner to power up and establish a connection.
Most modern scanners will display a menu or automatically begin scanning.
Step 3: Read the Diagnostic Trouble Codes (DTCs)
Once connected:
- Select “Read Codes” or a similar option on the scanner.
- The device will retrieve any stored trouble codes.
- Write down the codes (e.g., P0455 for a large EVAP leak).
These codes help identify the specific issue. For example:
- P0171: System too lean (bank 1)
- P0300: Random/multiple cylinder misfire
- P0420: Catalyst system efficiency below threshold
Use a code lookup tool or app (like OBD2 Code Lookup or RepairSolutions) to interpret the meaning.
Step 4: Fix the Underlying Issue
Before resetting the light, address the problem:
- If the code points to a loose gas cap, tighten it or replace it.
- If it’s a sensor issue, consider replacing the part or cleaning it (e.g., MAF sensor cleaner).
- For misfires, inspect spark plugs and ignition coils.
Never reset the light without fixing the cause—otherwise, it will likely come back on.
Step 5: Clear the Codes and Reset the Light
After repairs:
- On the scanner, select “Clear Codes” or “Erase DTCs.”
- Confirm the action when prompted.
- The check engine light should turn off immediately.
If the light remains on, the issue may not be fully resolved, or the system hasn’t completed its self-check.
Step 6: Perform a Drive Cycle
After clearing codes, your Fiat needs to run through a drive cycle so the ECU can recheck systems and confirm repairs.
A typical drive cycle for a 2015 Fiat includes:
- Start the engine and let it idle for 2–3 minutes (cold start).
- Drive at 30–40 mph for 5 minutes.
- Accelerate to 55 mph and maintain speed for 10 minutes.
- Decelerate slowly without braking (coasting).
- Repeat the cycle once or twice.
This allows the O2 sensors, catalytic converter, and EVAP system to be tested. If no new codes appear, the system should stay clear.
Method 2: Disconnect the Battery (Temporary Fix)
Disconnecting the battery is a quick way to reset the check engine light, but it’s not recommended as a first choice. It can erase important data like radio presets, clock settings, and adaptive learning values in the ECU.
Step 1: Turn Off the Engine and Remove the Key
Ensure the car is completely off and the key is out of the ignition.
Step 2: Locate the Battery
In the 2015 Fiat 500, the battery is under the hood on the passenger side. Open the hood and look for a black box with two terminals.
Step 3: Disconnect the Negative Terminal
Use a wrench (usually 10mm) to loosen the nut on the negative (-) terminal. Carefully remove the cable and tuck it away from the battery to prevent accidental contact.
Step 4: Wait 10–15 Minutes
This allows the ECU to fully discharge and reset. Some sources recommend waiting up to 30 minutes for a complete reset.
Step 5: Reconnect the Battery
Reattach the negative cable and tighten the nut securely. Start the car and check if the light is off.
Important Notes:
- The light may stay off temporarily, but if the issue persists, it will return.
- You may need to reset the radio, clock, and power windows.
- This method does not clear pending codes or complete drive cycles.
Use this method only if you don’t have access to a scanner and need a quick reset—preferably after fixing the issue.
Method 3: Drive Until the Light Turns Off (Not Recommended)
Some drivers believe that simply driving the car will make the check engine light disappear. While it’s true that some minor issues (like a loose gas cap) may resolve on their own, this is unreliable and risky.
The light will only turn off if:
- The problem is fixed.
- The ECU completes a drive cycle and confirms no faults.
- No new codes are generated.
However, if the underlying issue remains, the light will come back on—sometimes within minutes. Relying on this method can lead to:
- Worsening engine damage.
- Failed emissions tests.
- Increased repair costs.
Always diagnose and fix the problem first.
Troubleshooting Common Issues
Even after resetting the light, you may encounter problems. Here’s how to handle them:
The Light Comes Back On Immediately
- This means the issue wasn’t fixed. Recheck the trouble codes.
- Inspect sensors, wiring, and connections.
- Ensure the gas cap is tightened properly (turn until it clicks 3 times).
The Scanner Won’t Connect
- Check that the ignition is on.
- Ensure the OBD2 port is clean and undamaged.
- Try a different scanner or update the software.
The Light Flashes While Driving
- A flashing light indicates a severe misfire that can damage the catalytic converter.
- Pull over safely and turn off the engine.
- Call a tow truck and have the car inspected immediately.
No Codes Are Found, But the Light Is On
- Some scanners may not read manufacturer-specific codes.
- Use a professional-grade scanner or visit a mechanic.
- Check for pending codes—these are stored but haven’t triggered the light yet.
Preventing Future Check Engine Light Activations
An ounce of prevention is worth a pound of cure. Keep your 2015 Fiat running smoothly with these tips:
Use High-Quality Fuel
- Fill up at reputable stations.
- Avoid ethanol-blended fuels if possible (though E10 is generally safe).
- Use fuel injector cleaner every 3,000–5,000 miles.
Replace the Gas Cap Regularly
- Inspect the cap for cracks or worn seals.
- Replace it every 5 years or if it doesn’t click when tightened.
Follow the Maintenance Schedule
- Change the oil every 5,000–7,500 miles (or as recommended).
- Replace spark plugs every 30,000–40,000 miles.
- Inspect air and cabin filters regularly.
Keep the Engine Clean
- Clean the MAF sensor with MAF cleaner every 15,000 miles.
- Check for vacuum leaks in hoses and gaskets.
Monitor Driving Habits
- Avoid short trips that prevent the engine from reaching operating temperature.
- Don’t ignore warning signs like rough idling or poor acceleration.
When to See a Mechanic
While many check engine light issues can be resolved at home, some require professional attention. Visit a certified mechanic if:
- The light flashes or stays on after repairs.
- You’re unsure how to interpret or fix the trouble code.
- The car is running poorly, overheating, or making unusual noises.
- You need emissions testing and the light is on.
A professional diagnostic can save time and money in the long run.
Conclusion
Resetting the check engine light on a 2015 Fiat is a manageable task—if you approach it the right way. The key is to diagnose the problem first, fix it properly, and then reset the light using a reliable method like an OBD2 scanner. While disconnecting the battery or driving the car might seem like quick fixes, they often lead to recurring issues.
By following this guide, you’ll not only clear the light but also ensure your Fiat runs efficiently and safely. Remember: the check engine light is your car’s way of asking for help. Listen to it, address the issue, and keep your 2015 Fiat in top condition for years to come.