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How Can I Reset My Check Engine Light?

Automotive code reader.
A loose gas cap can cause the check engine light to come on.
A problem with a spark plug can cause the check engine light to come on.
When the check engine light goes on, check under the hood for frayed wires that may need to be fixed right away.
A ScanGuage or other OBD-II code reader can reset the check engine light if the issues have been repaired..
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  • Written By: Ken Black
  • Edited By: Bronwyn Harris
  • Last Modified Date: 09 October 2014
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There are a number of ways to reset a check engine light, but some methods may be better than others. In some cases, it may be possible to turn the light off by using a diagnostic scanner, which attaches to the car and provides information on what has caused the light to come on. Disconnecting the battery may also temporarily turn the light off. The check engine light often indicates a serious problem with the car, however, and the best way to turn it off is to fix the underlying issue.

When the Light Comes On

Officially known as a malfunction indicator lamp, the check engine light can go on for a number of different reasons. In some cars, something as simple as a loose gas cap, which the car's computer can read this as a leak in the emissions system, or even a change in humidity can cause the light to come on. Most of the time, it lights up to warn about a problem with the engine or emissions system, which should be investigated relatively quickly. If the check engine light is red instead of yellow or if it's blinking, it's usually a sign of a serious problem that should be dealt with as soon as possible.

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Experts often recommend checking the cap on the gas tank first; if it's loose, tightening it should cause the light to go off after a day or two. Sometimes, a gas cap gets lost or breaks, but replacing it is usually a quick and inexpensive repair. You should also check under the hood to make sure there aren't any obvious problems like a leaking hose or frayed wires that need to be fixed before they get worse and cause the car to stop running.

Check the Error Codes

When the check engine light goes on, an error code is saved in the car's computer. With the right tool, called an automotive diagnostic scanner or a code reader, you (or a mechanic) can read this code and find out what's wrong with the vehicle. Relatively inexpensive code readers are available, some for less than $100 US Dollars (USD), but an automotive parts store or repair shop may be willing to check the code for free. These readers may also be able to clear the code from the computer, in some cases, turning the light off quickly and easily.

Disconnect the Battery

In some cars, especially those made before the mid-1990s, you can reset the check engine light by disconnecting the battery. Newer vehicles have a feature that will simply turn the light back on after the battery is reconnected if the car is not drained of electricity properly, however. You can do this by constantly blowing the car's horn until it dies or turning on the headlights, then waiting several minutes. This will ensure all electrical current has been drained from the car's capacitor. At this point, it should be safe to reconnect the battery and the check engine light should not longer be lit.

Disconnecting the battery will erase all the data from the vehicle's computer, which could make any problems with the car more difficult to diagnose in the future. It will also reset the electronic systems inside the car; if the car has an anti-theft radio system, for example, it will likely go into safe mode and will need a code to unlock it. All radio station presets will also need to be reprogrammed.

If you're trying to turn the light off in hopes of passing an emissions test, this method rarely works. Even if all emissions data is cleared from the computer when the battery is disconnected, the car's systems need to complete a series of tests called a "drive cycle" before it can pass testing; sometimes more than one drive cycle is needed before the car is ready. The chance of the car completing its internal tests and the light not coming back on before the emissions test on is very small.

Fix the Car

The best way to turn off the check engine light is to fix whatever problem has caused it to come on in the first place. Even if you were able to turn it off by clearing the codes or disconnecting the battery, if what caused the light to come on hasn't been corrected, it probably won't stay off for very long. Postponing a repair by ignoring the car's warning is usually a costly mistake; a problem that could have been fixed easily early on could grow into a major repair if it's not addressed in time. Unless you're comfortable checking the error codes and doing repairs yourself, it's best to take the car to a mechanic and get it fixed.

Service Required Light

Sometimes, drivers confuse the "Service Required" warning with the check engine light. In most vehicles, these two warning lights mean different things. The service engine indicator means that the car is due for routine maintenance or an oil change. Its intervals are typically set by mileage, not because the car's computer detects anything wrong.

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Discuss this Article

anon925496
Post 25

I agree that this system of failing emission tests and thereby refusing tag renewal for a check engine light being on, is a rip off! There should be a system in place that dictates if the car is dangerous on the highway or not. Period. Not whether you need something like a gas cap or a tune up. These lights are referred to as "idiot lights" because the people who put the system in place are either inept or lazy and use a light to inform you something may need checking. Unacceptable!

anon313869
Post 23

The OBD II’s Actron autoscanner is compatible with OBD II standard vehicles, light trucks, SUV and minivan. It is designed with extensive OBD II code library built-in units. Another notable feature is its sheer size, which makes it simple for owners, like backlit screen reading.

anon285378
Post 21

The ABS light and the check engine light on my 2007 Toyota Axio is on. The problem is that when the diagnostic scanner is connected to the vehicle, it does not show any result. Kindly tell me what would be the problem then. Either it's the car plug (socket) problem or wiring or something else. --ibad

anon268790
Post 20

I just had my engine and alternator replaced on my 2006 Toyota Avalon. On the dashboard there are two small red lights blinking: the gas tank light and a car indicator light. How do I turn those lights off or reset without having to return to the dealership?

anon266659
Post 19

You press the horn while the battery is disconnected to drain out any residual charge left in the computer.

anon260146
Post 18

The advice you offered regarding the check engine light by disconnecting the battery and the sounding the horn until all the electricity is drained from the capacitor, then reconnecting the battery is redundant! How does this work when the horn needs the battery to sound?

anon253760
Post 17

I have a 1999 mercedes van 312 model lwb. The edc light is on but it has put itself into safe mode for power and won't go above 3000 rpm. Please help. I've tried disconnecting the battery twice but still nothing.

anon240552
Post 16

This system of not allowing someone to pass inspection because of a check engine light is an abomination and a total scam ripoff. I hope these state governments, the auto repair shops, and everyone else involved in this hustle lose their shirts when the american public wakes up and turns on them. This system is a joke.

anon232157
Post 15

Worked for me for my 99 Plymouth Breeze. However, the car failed inspection because I took the car in right after clearing the light. Looks like I need to drive it some unknown number of miles before the computer will let my car pass. Ugh.

anon165308
Post 14

Disconnecting the battery on my 1992 Geo Tracker cleared the code.

anon154597
Post 13

i have a 2004 nissan altima with mileage 100 k and my check engine light just came one. i just want to know is it anything major. thank you.

anon150883
Post 11

Always remember to find out why it is on. There are many ways to shut it off, but none will fix the actual problem.

anon145588
Post 10

The check engine light can come on for many reasons, some as simple as the air filter needs to be replaced or something more serious like engine failure from an internal engine component failure.

If it comes on, you should not look for simple instructions of "how to reset it." It will come right back on if the mechanical problem has not first been resolved! You also are subjecting the vehicle to more serious issues by not resolving the first indication somethings wrong.

The check engine light was first associated with the emissions, but has since been reconfigured to access other problems as well.

You should also keep in mind you have a "brain" which controls and records everything about the vehicle---It's the computer! The dealer can connect your car to the shop scanner and see everything you have done with the vehicle from speed to erratic driving habits to oil changes-its all there just like your home desktop or tower unit.

So when the check engine light comes on, don't just attempt to reset it. First, find the reason it came on through a means of diagnostics like a hand held OBD scanner or have a repair shop investigate, but do not just reset the light. You are asking for big trouble and more likely than not, a bigger problem that means more expense to repair!

anon135376
Post 9

I checked a shop and they said 97 dollars to reset. What a ripoff. So I bought a reader for 147 dollars taxes included and reset. Question: If there is something wrong with the exhaust gas recirculation will the light come on again?

anon131522
Post 8

Thanks for the advice. I've read similar articles and think I'm going to purchase an inexpensive auto scanner just in case some other light comes on. I have a 1996 Mercedes. Will check back later with an update.

anon126275
Post 7

Thank you so much for this. my service engine light just came on but my change oil soon light has been on for a while. I pray it's just time for an oil change and that's the reason for the engine light coming on. I have a 2000 buick lesabre custom and I think it's set for the oil to get changed in mileage intervals. Thanks.

anon108311
Post 6

i just got my car checked out and got an oil change, transmission fluid cleaned and everything and my check engine light is still on. i don't see any problems with the car and wasn't told it had any when i got it checked, why is it still on?

jwalker222
Post 5

I have a 91 acura legend and tried this several times and it didn't reset. The vehicle will not start until the light goes off. any suggestions? I would like to get it started to get it to a mechanic today!

anon61820
Post 3

it did not work for me. i disconnected the battery for at least 45 minutes and pressed on the horn and the dome light came on. I did this twice and what a waste of time. now I have to go to a mechanic to have it diagnosed. I have a 05 honda accord coupe.

anon47501
Post 2

Great article. Whenever I purchase a "used" or "pre-owned" vehicle, I always do the disconnect battery process, simply because I don't know how the previous owner drove the vehicle. By resetting it, I'll know the car will be "learned" for my habits :)

anon29798
Post 1

Thank you so much for the suggestion of actually draining the battery after disconnecting it. I have been trying for a week to clear a code and I finally got it cleared thanks to you!!! Sometimes it's the easiest solution that we overlook.

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