How do I get my check engine light to go out?

The check engine light goes out once the underlying fault is addressed and the vehicle’s computer clears the stored fault codes, typically automatically after a few drive cycles or manually with an OBD-II scanner. If the light is blinking, stop driving and have the car checked immediately.

This guide explains what the light means, common causes, how to diagnose with an OBD-II tool, and when to seek professional help to ensure your car runs safely and cleanly.

What the check engine light means

The malfunction indicator lamp (MIL), better known as the check engine light, signals emissions-related or engine-control faults detected by the on-board diagnostics system. A steady light usually means a fault has been detected; a blinking light indicates a severe issue such as a misfire that can damage the catalytic converter. In either case, addressing the fault promptly helps protect the engine, fuel economy, and the environment.

Common causes of a check engine light

Most CEL codes point to sensor faults, loose connections, or emissions system issues. Here are the frequent culprits you may encounter.

• Loose or damaged gas cap


• Faulty oxygen (O2) sensor


• Faulty mass airflow (MAF) sensor


• Failing catalytic converter or related emissions components


• Worn spark plugs or ignition coils


• Vacuum leaks in hoses or intake manifold


• Exhaust leaks or damaged exhaust components


• Malfunctioning EGR valve or emissions-control hardware


• Electrical wiring or sensor connectors corroded or loose

Conclusion: While the CEL can be triggered by a minor issue, it’s best to read the diagnostic trouble codes (DTCs) to identify the exact cause before driving far. A blinking light is more urgent and requires immediate attention.

How to diagnose and clear the light

Before attempting any repairs, read the fault codes and follow up with appropriate checks. Many shops and auto parts stores offer free code scanning that can guide your next steps. Here is a practical process you can follow:

1. Plug in an OBD-II scanner and read the stored fault codes (DTCs).


2. Note the codes and look up their meanings in a repair manual or reputable online database.


3. Inspect the most common causes first (gas cap, visible leaks, damaged hoses, or loose connections) and address them as needed.


4. If a component replacement is required, perform the repair or have it done by a qualified technician.


5. Clear the codes with the scanner (or use the vehicle’s built-in reset procedure if your manual describes it).


6. Take the car for a careful test drive to allow the ECU to recheck the system and monitors.


7. Re-check for codes after driving; if the light returns, review the repair or revisit the diagnosis.


8. Call a professional if the light stays on or you notice symptoms such as rough running, reduced power, or stalling.

Conclusion: Clearing the codes and ensuring the fault won’t recur is the key to turning off the MIL. If you cannot identify or fix the fault, professional diagnosis is the safest course.

When to seek professional help

Even common issues can require expert diagnosis, especially if the light returns after repair or if you see warning symptoms like misfiring, poor acceleration, or unusual noises. A technician can perform a full diagnostic, perform emissions tests if needed, and ensure the repair is done correctly to avoid harming the catalytic converter or other systems.

Summary

The check engine light turns off once the underlying fault is fixed and the vehicle’s computer clears the stored fault codes. Start by reading the codes with an OBD-II scanner, address the identified issue (gas cap, sensor, leak, etc.), and clear the codes. Then drive normally to confirm the issue does not reoccur. If the light stays off after repairs, you’re likely good to go; if it returns, re-diagnose or seek professional help.

Can a check engine light go away by itself?

Yes, a check engine light can clear itself if the underlying issue is resolved, but it won't happen immediately. The light typically goes off after a few driving cycles—where the car is started and driven for a certain distance—if the computer no longer detects the problem. For example, a loose gas cap can trigger the light, and after it's tightened, the light may turn off on its own after some driving.
 
How it works

• The vehicle's computer monitors various sensors to detect issues. 
• A minor or temporary fault, like a loose gas cap, can trigger the light. 
• If you fix the problem (e.g., tighten the cap), the computer will continue to monitor the system. 
• Once the vehicle has completed a certain number of "drive cycles" (a specific combination of driving and stopping), the computer will recognize the issue is gone and turn the light off automatically. 

This video explains how to reset a check engine light using several DIY methods: 1mAuto EducateYouTube · Apr 14, 2025
What to do if the light comes on

• Check the gas cap: This is a very common and easy fix. Remove it and re-tighten it until it clicks. Then, drive for a while to see if the light turns off. 
• Drive and wait: If the issue was temporary (e.g., a brief sensor reading out of range), the light may go off on its own after a few days or about 30–50 miles of driving. 
• Get the codes read: You can buy an inexpensive OBD-II scanner to read the specific trouble code that is causing the light. Many auto parts stores also offer this service for free. This will tell you exactly what the problem is. 

Important note

• If the check engine light comes back on, even after it had gone off, it indicates the problem is still there and needs to be addressed professionally. 
• If the light is flashing, it indicates a severe misfire, and you should pull over and have the vehicle towed to a mechanic. 

How long does it take for a check engine light to turn off?

A check engine light may turn off on its own after 2–3 driving cycles (roughly 50–100 miles) if the problem was minor and the condition has been corrected, such as tightening a loose gas cap. However, if the issue is more serious, such as a faulty sensor, the light will not go off until the underlying problem is repaired and the code is cleared, often with a scan tool. 
This video demonstrates how to reset your check engine light using simple methods: 44sAuto EducateYouTube · Apr 14, 2025
For minor issues

• Driving cycles: The car's computer will perform a series of "driving cycles" to test emissions systems. If the problem is resolved, the light will typically turn off after about 50–100 miles of mixed driving. 
• Examples: This often works for issues like a loose gas cap, which is a common reason for a check engine light. 

For major issues

• Repairs are necessary: If the light is on due to a faulty part like an oxygen sensor, it will not turn off on its own. 
• Code clearing: After the repair is made, a mechanic or the car owner will need to use an {nav}OBD-II scan tool{/nav} to clear the code and turn the light off. 
• Light reappearance: If the light comes back on after a repair, it suggests the problem was not fully addressed and may require further diagnosis. 

Manual reset methods

• Disconnect the battery: Disconnecting the negative terminal for a few minutes can often reset the light, but this will also clear the code and should not be relied on if the underlying problem is not fixed. 
• Use a scan tool: The most effective method is to use an OBD-II scan tool to read the code, fix the problem, and then clear the code. 

Important consideration

• Do not ignore the light: Even if the issue seems minor, it is best to have the vehicle inspected to prevent potential damage or to ensure it passes an emissions test. 

How to pass emissions test tricks?

To pass an emissions test, warm up your engine, perform routine maintenance like changing the oil and air filter, and ensure any "Check Engine" light issues are fixed beforehand. Driving the car enough to meet the readiness requirements after maintenance is also crucial. 
This video explains several ways to pass an emissions test, including preparing your car before the test and driving it to ensure readiness: 45sRatchets And WrenchesYouTube · Dec 1, 2015
Preparation and maintenance

• Fix the "Check Engine" light: Your car will fail if the light is on, so resolve any related issues before the test. 
• Perform routine maintenance: Get a tune-up, change the oil and air filter, and replace spark plugs to help the engine run more efficiently. 
• Check the gas cap: Ensure the gas cap is tight and not cracked, as loose caps can trigger a "Check Engine" light for an evaporative emissions system leak. 
• Consider fuel additives: Using a fuel or injector cleaner before the test can help clean out carbon deposits. 

Before and during the test

• Warm up the engine: Drive your car for at least 20 minutes to warm it up. A hot engine runs more efficiently, and the catalytic converter needs to reach a high temperature to work correctly. 
• Drive to meet readiness requirements: After any repairs or maintenance, you need to drive your car to allow its onboard computers to complete diagnostic tests known as "monitors". This can take anywhere from 60 to over 200 miles depending on your vehicle and driving conditions. 
• Inflate tires: Properly inflated tires reduce rolling resistance, which can lead to better performance and emissions. 
• Maintain a full tank: Having a gas tank that is between a quarter and three-quarters full can help with the readiness test cycle. 
• Keep the engine running: If possible, keep the engine running while you wait for your turn at the test center. 

How many miles do you have to drive to clear a check engine light?

You need to drive between 30 and 100 miles, with a mix of city and highway driving, to clear a check engine light after it has been reset. Driving this distance allows the vehicle's computer to complete a "drive cycle" and re-run its diagnostic tests, which is necessary for clearing the light and for the vehicle to pass an emissions test. 
This video explains how to clear a check engine light and what to do after: 1mMechanic BaseYouTube · May 24, 2023
Mileage and driving conditions

• Average/Mixed driving: 50 to 100 miles. 
• Mostly highway driving: You may need as few as 30 to 50 miles, as long as you have a mix of speeds. 
• Mostly city driving: You may need 80 to 100 miles. 
• Drive cycles: Instead of driving one long trip, it's better to take several shorter trips to complete the cycle. This typically involves starting the car, driving, and then turning it off and on again multiple times.