Kate is a research enthusiast with a Bachelor of Science degree from Sonoma State University. Kate has a passion for the automotive field.
Why Is My "Check Engine" Light On?
You've fixed the issue that made your "check engine" light turn on, but now it won't turn off! This may not be your fault. Sometimes the computer in your vehicle will need a little help to see that the issue has been resolved. I'll go over a few techniques for resetting your check engine light.
This light displays itself when the onboard computer system recognizes an electrical or mechanical problem with your vehicle. When the problem is fixed, the engine light does not always turn off. This can be annoying, cause you to fail an emissions (smog) test, or keep you from finding out about future problems the vehicle's computer might be trying to alert you to.
Of course, it is essential to be sure that the light isn't on because your engine really does still have a problem. Try one (or more) of the following approaches to turn the light off. If it does not go off, then your engine has a problem.
4 Ways to Reset the "Check Engine" Light
1. Drive your car and let light go off by itself.
2. Turn the engine on and off three times in a row.
3. Disconnect and reconnect the battery.
4. Use an OBD code reader.
Wrench and OBD reader
1. Drive Your Car and Let the Light Go Off by Itself
The first and easiest method for clearing the check engine light is driving and time. Most onboard computers will recheck whatever problem caused the check engine light to activate multiple times. Drive your car as you normally would.
If the check engine light is still on after three days, your problem may not have been fixed or you may need to try some of the methods below to reset it.
2. Turn the Car On and Off Three Times
Some vehicles will automatically reset the trouble codes that caused the initial error after the vehicle is turned on and off three times in succession. To do this, insert your key into the ignition, turn the vehicle on for about a second, and then off for about a second. Repeat this two more times then drive the car as normal. Check to see if the check engine light reset.
3. Disconnect and Reconnect the Battery
You will need a wrench. Prop open the hood and use the wrench to disconnect the positive power cable to the vehicle battery. Leave the battery disconnected for at least 15 minutes. Then put your key into the ignition and turn it three times to the “ON” position. This will clear the emissions data from the vehicle memory as well as the readiness flag data.
Reconnect the positive battery cable and turn the key in the vehicle ignition. Wait one minute and the check engine light error should be gone.
4. Use an OBD Code Reader
You will need a wrench and an OBD (onboard diagnostic) reader. These inexpensive readers analyze and clear engine codes. I have used the Kobra OBD scanner with great success many times for this task.
To perform this method:
- Plug the reader into the OBD port of your vehicle. This port is usually located on the underside of the dash area just above the foot well. On some vehicles, you'll have to remove the door on your fuse box to access this port.
- Once you have connected the reader, press the "enter" button to turn it on.
- The device will scan your engine for any error codes. Once done analyzing, the reader will display any error codes it finds. Make note of the codes (if any) if you wish to cross-check them in the code reader's manual or online.
- Now you can press the "scroll" button to find the option to erase the code. Press enter while on this option to erase the fault code and reset the check engine light.
Frequently Asked Questions
Here are just a handful of commonly asked questions related to this issue.
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Can the check engine light turn off by itself?
Yes, sometimes the light will turn off by itself as you drive it around for a while after addressing the issue that made it turn on in the first place.
Why does my check engine light turn on and off intermittently?
There could be a few reasons why this is happening. A loose gas cap, failing engine sensors, bad spark plugs, faulty valves such as in the EGR (exhaust gas recirculation) system, or intermittent misfiring could all be potential culprits. In this case, it's often best to take your car into a mechanic shop to get a diagnostic, or at the very least use an OBD reader yourself.
Does the check engine light turn off automatically after repair?
Sometimes yes and other times no. If the issue has been repaired and the computer has been cleared with a scan tool or code reader, then the light should turn off relatively soon after.
That's not always the case though, and the light may still stay on (or turn on and off intermittently)—especially if you have a larger electrical or wiring problem.
If you got your car repaired at a mechanic shop and the issue seems to be resolved but the light remains on, however, then you should take it back to the shop and ask the mechanic if they can reset the light.
Do I need a special tool to turn off my check engine light?
Yes. If you want to turn off your check engine light yourself, then you will need an OBD code reader. It plugs into the diagnostic port commonly located under the dashboard in cars made in 1996 or after. These devices can be purchased at various automotive parts stores or online at various retailers such as Amazon.
Be advised, however, that if you use an OBD reader to clear the code but the issue has not actually been resolved, then the check engine light will likely turn back on again sometime soon thereafter.
These Techniques Should Help You Reset Your Check Engine Light
Following these techniques will allow you to rid the annoying check engine light as well as allow for new problems to be displayed properly.
Whether you choose to manually reset the onboard computer by resetting the battery or by using an OBD reader, you will be able to successfully fix the error. You may use these techniques to fix the check engine light error as well as any other errors in the future should they present themselves.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Why did my check engine light come on after I replaced some fuses?
Answer: Likely one of these situations occurred:
1. You replaced a fuse with a fuse of an incorrect value. Double check that you used the correct type of fuse per the vehicle's manual.
2. One of the fuses you inserted is bad or quickly went bad after installation, causing one of the systems in your vehicle to stop working correctly.
3. You replaced a bad fuse, causing a system in your vehicle that was not working previously to start working. That system has an issue causing your vehicle to display the check engine light. This is less likely if the check engine light wasn't on before this.
4. It's a coincidence and another system in your car started to experience an issue just after you replaced the fuse. Believe it or not, this does happen even though it is also less likely.
The easiest way to narrow down the problem is to use an OBD 2 reader, such as the one I linked to in the article, to read the trouble codes from your car's computer. You can then cross reference this code online or with the manual that comes with the reader to find out exactly which system is causing your car's check engine light to illuminate.
Question: Can I get rid of the "check engine" light without an onboard diagnostic reader?
Answer: You certainly can, but it may be more difficult. I would start by trying the other methods outlined in this article. If those don't work, then there is likely something mechanically wrong with the vehicle.
It can be as simple as replacing an easy to reach $10 sensor that has gone bad, or much more difficult. While some expert mechanics can troubleshoot their vehicle and locate the issue without the assistance of an OBD reader, most people (such as myself) need a code reader to make things easier for us.
A code reader can help you by manually allowing you to clear the fault code that has caused the check engine light to illuminate (in case it was stuck on due to an error in the car's computer), or if there truly is something mechanically wrong then it can give you the "error code" that your car is producing.
This error code is the actual reason the check engine light has been activated. You can then look up this error code in the reader's manual or online and see what the issue is with your vehicle in plain English. It is a handy tool that even most expert mechanics quite heavily rely on these days.
Question: I replaced my vehicle's O2 sensor, disconnected and reconnected the battery multiple times, and even changed its plugs, yet the check engine light came back on after a 45 km drive. What should I do next?
Answer: If your car is 1996 or newer model, you should connect its computer to an OBD2 reader to find out what error code it's generating.
Once you get this code, you'll be able to translate it and gain a better understanding of what is wrong with your vehicle.
If it says it is "out of range," which is very common when a sensor malfunctions, replace the faulty sensor. Then take the steps outlined in this article to reset the check engine light.
© 2012 Kate Daily