The "Service Engine Soon" Light on Your Dash Might Just Mean a Faulty Gas Cap

Oh, No! My Check Engine Light Is On!

The purpose of the "service engine soon" light is to warn the operator that sensors in the vehicle have detected a malfunction. When we first see this little light on our dash we get a little worried at the potential cost of the repair. Immediately we assume the worst and fear a bill in the hundreds or thousands of dollars. It's true there may be a major problem with the engine or one of its components, but often it is something that can easily fixed by the car's owner.

What Is the Purpose of the "Service Engine Soon" Light on Your Dash?

The initial effect of seeing this little light on your dash is to scare the living gezebbes out of you. Immediately you assume the worse and fear that you must spend hundreds or thousands of dollars to "fix" your car.

The intended purpose of the "service engine soon" light is to warn the operator of the vehicle that a malfunction has been detected by sensors in the emissions system of the vehicle. There may be a major problem with the engine or one of its components, but it's usually a minor issue.

First, Check Your Gas Cap

The culprit could be as simple as having a loose or faulty gas cap. Before you drop hundreds of dollars at the garage, tighten the gas cap, make sure your gas tank is more than half full, and then drive for about half an hour. If the light does not go off, try buying and installing a new gas cap. They cost less than $10 at your local car parts retailer. It is worth ruling out this common problem before proceeding to bring in the vehicle for an expensive service call.

It Wasn't the Gas Cap?


Well, I know people who tell me that their light has been on for the last five years! I personally wouldn't go that long without doing something about it. If the light is on solid, you most likely have an emissions issue, not necessarily urgent, but one it would be wise not to avoid. If the light is blinking, you have an urgent issue and must go immediately to a garage.

The problem could also be something like the oxygen sensor, which monitors how much unburned oxygen is being released with the exhaust. Not changing the oxygen sensor promptly may cause damage to your catalytic converter, a part that could cost as much as $2000, while an oxygen sensor may cost from $20 to $120 depending on your vehicle. If you are "handy" it may be possible for you to change the oxygen sensor yourself. The procedure is usually detailed in your owner's manual; it is usually as simple as removing the old sensor and popping the new one in. Doing it yourself will cost you much less than going to a garage.

Other problems could be a dirty or defective MAF (Mass Air Flow) sensor). A possible cause of a dirty or defective MAF sensor is failing to change your air filter, or installing the air filter improperly. You can try to buy a can of MAF sensor cleaner for $10, but a word of caution as these sensors are very fragile. A new sensor can cost between $75 and $200, depending on your car model, and is easy to install.

Another possible culprit triggering the "service engine soon" light is misfiring spark plugs. Spark plugs on older vehicles (before 1996) needed to be changed every 40,000 to 50,000 kilometers; on more modern vehicles spark plugs can go to 150,000 km before needing to be changed. Faulty spark plugs can cause your engine to misfire. If you feel your engine falter occasionally, or the engine has a jolty feel under acceleration, your engine is misfiring and throwing off your fuel efficiency.

So how do you know for sure whether it's spark plugs, MAF sensor, or something else?

Get an OBD II Scanner

You've ruled out the simple, common causes and your light is still on. You now have two choices:

  • Bite the bullet and bring the car to the mechanic. You car will be fixed and your mechanic's kids will have a nice Christmas.
  • Or, you can at least do some of the investigative work yourself by getting a code-scanning device.

A code scanner or OBD II (On Board Diagnostics II) scanner ranges from $10 on eBay to $200+ for a really good one at your local auto parts store. The savings can be tremendous after a couple of "service engine soon" light incidents. The initial cost of a mechanic's visit will start at $100 just to get the error codes from your car's onboard computer. Add a couple hundred for labour and inflated costs for parts, and your mechanic is happy to see you every time.

Or you can spend money once on the OBD II code reader, get the real low down on what is happening for yourself, find your own parts, and save a bundle. The cost of the OBD II code reader will cover itself with every error light incident. It can also be used on several cars to maximize savings.

If you are not comfortable with the installation of certain parts, you can do your own diagnostics, buy the parts yourself, and leave the installation to the mechanic; you will still save at least 50% of what it would have cost if you left it all to the mechanic. Hey, he's gotta eat, you know?

© 2012 Ardot

Comments 33 comments

dmvjane profile image

dmvjane 3 years ago from Philippines

I might use some of the information in this hub in the future. Great work though.

TruSoulDJ 3 years ago

Thanks for this article. My light HAS been on 5, well, maybe 3 years.

Ardot profile image

Ardot 3 years ago from Canada Author

Wow! TruSoulDJ, did you get the light to go out?

jenb0128 profile image

jenb0128 3 years ago from Michigan

Great information! My light came on the other day and I did the gas cap check, but the light's still on. I didn't buy a new gas cap though - I'll have to try that before taking it in to the shop.

Ardot profile image

Ardot 3 years ago from Canada Author

I hope it's nothing to serious! After you check or change your gas cap you should have at least 3/4 of a tank of gas and depending on your car, it takes between 20 and 40 minutes of driving for the pressure in the tank to go back to normal. At that point the light will go out, if it's the cap.

Thanks for reading!

Brian 3 years ago

I am not going to pay a mechanic $100 to do an error code check, when I have a Dodge. Ina Dodge just turn your key,on,off and codes will show on dash. :)

Lucky for now 2 years ago

It fixed itself? Had my check engine light on as of after 5 mins of driving it on a Saturday. It felt like it was not running on all the cylinders, jumpy at a stop light and revs were low. I was nearly on E. Filled it up Monday on the way to work, Tuesday afternoon car is running normal and light is off. LOL - Gotta love cars, wish we could fix ourselves like that!.

angie 2 years ago

I just fix my car cause the check engine soon light came on and today its back on why

Ardot profile image

Ardot 2 years ago from Canada Author

Hi Angie, What was wrong with your car?

earkwell 2 years ago

It's OBD not ODB... Good effort though

Ardot profile image

Ardot 2 years ago from Canada Author

Thanks earkwell! Makes perfect sense now.... OBD On Board Diagnostics.

Andy 2 years ago

Great post. I came across a very similar article on is it true that it can take up to 200 miles for your light to trigger?

Ardot profile image

Ardot 22 months ago from Canada Author

Hi Andy, Thanks for liking my artilce, Yeah it takes a while for the light to go on, as well as off. With the gas cap scenario, I think it has to do with the pressure in the tank, when the cap is loose, the pressure drops and triggers a sensor that there's an emissions problem.

I looked at the article you mentioned as being similar, I found it to be very brief in comparison to mine. We do share some of the same terminology, but it's all common knowledge.

Lisa 22 months ago

It eased my mind a little to know that it isn't as urgent if the "service engine soon" light is constant instead of blinking.

Daniel 21 months ago

Have similar problem with my SUV. And after 10 days or so, the light was off. I noticed that when I'm driving/speeding on the highway, the light goes off. My friend has a scanner and the code read 0304, which implies catalyst converter problem. But right now no light. .... what do you think guys ?? My car is due for spark plug change. Could this be a reason. .. ??

Carolyn 20 months ago

Add Your car got stuck in snow and trying to get it out my car started over heating and my check engine light came on what do u think ? It's a 2002 ford mustang I don't believe my fan was working.

Ardot profile image

Ardot 20 months ago from Canada Author

Hi Carolyn.... not sure, is your car ok now?

You should have a competent mechanic look at it. Keep in mind if it's a flashing engine light you're problem is more severe than if it's on solid.

Could also be your coolant....

Mel 19 months ago

Hi... My service engine soon light came on like 3 weeks ago.. I took it to the mechanic and they replaced the Map Sensor, the camshaft sensor, spark plugs changed and the light still comes back on. It's off for a little bit after each service but the light still comes back on. I can't afford to keep spending money and not getting the issue resolved.. I'm at a loss and suggestions?

Ardot profile image

Ardot 19 months ago from Canada Author

Hi Mel, I wonder, did you try changing the gas cap? I'ts a $10 fix worth trying. If not, I know may people who've been going for years with the light on, they don't seem concerned as their cars are close to the end of their useful life...

Mel 19 months ago

No I haven't tried changing it, I guess I can try that and see If it works.

Thank you

Sandy 19 months ago

Hi. I have Nissan altima 2000. My car dashboard is showing solid service engine soon from last 6 months. When I go to mechanic, he use to say ignore it. But I always use to afraid before driving. How can I get rid of it?

Ardot profile image

Ardot 19 months ago from Canada Author

Hi Sandy. If your mechanic says to ignore it, then you can simply disconnect your battery and reconnect it. This will flush out the error code causing the light. However you will lose all your radio presets and if the original problem still exists the light will come back on...

Just curious, did you try just changing your gas cap? I had a 2006 Versa that had a bad gas cap. Changed it and the light went away after 45 minutes of driving on an almost full tank.

Rose 18 months ago

Glad that I googled "service engine soon light". I was thinking when the light came one, OMG thousands of dollars that I don't have. My car is 15 years old and I pray that it last another 10 years. I am not concerned about the light after reading this. My stress level went down. I will do the gas cap thing and go from there.


Ardot profile image

Ardot 17 months ago from Canada Author

Hi Rose, do try the gas cap thing, but if that doesn't work you should definitely get it checked out... You don't want to be driving in an unsafe car that could let you down at any moment! Especially seeing that it's a 15 year old car...

Đ per 16 months ago

Every time I use chevron gas , my service soon light comes on

At 1/2 tk gas

deedee 15 months ago

Thanks, not so in the dark now.

PDXBuys profile image

PDXBuys 14 months ago from Oregon

This is exactly what happened to me last October. I have a 2006 Toyota Scion XB. The dash lights lit up light a Christmas tree. What did it mean? I was in a total panic and had visions of a repair costing thousands of dollars. Took it to an AutoZone store and the employee ran the diagnostic for free. First suggested fix was to replace the gas cap. Just cost a few bucks. Took a day for the pressure sensor to settle down but it worked!

GMG 11 months ago

No need to spend money on OBD scanner, simply watch this youtube and check out the sensor issue yourself.

Once you pump your gas in this manner, your light will begin to blink. Count each blink and you'll get the service code #, then check what the internet says is the cause. You can reset the service light yourself and it turns off. If the light comes back on right away then there's an issue, if not maybe just a fluke. My engine light came on and I didn't want to spend the money to figure it out, without reason, so I investigated it myself and reset it. Last 7 months car ran fine with no issues. Light just came on again tonight with exact same code. I repeated the steps and light's off now. Mechanic said car has no issue. Mine is a 2004 Nissan Sentra, perhaps its just showing its age.

Ardot profile image

Ardot 11 months ago from Canada Author

Awesome GMG!

Nissan huh, I had an '06 Versa that had so many issues.... I won't be getting another Nissan anytime soon.

Thanks for the service code hack!

William B 11 months ago

I have an 04 Chevy check engine light just came on a few days ago.I will try the gas cap thing...

ray 5 months ago

have a 97 caddy my service light has come on once every 6 months I got into the habit of disconnecting my battery then light goes off does not come back on car runs great I've been doing this for about 2 years dealer does oil changes and doesn't find nothing wrong but I don't mention light if I did ide be paying who know how going to get a scanner with all the money I saved. thanks for your post about OBD scanner.

Barbara 5 months ago

My service light has been on for 8 years. I take it to an auto supply store and they check; it is nothing big; I wonder, tho, if this is why my mileage has gone down on my 1996 Dodge Caravan with 290,000 miles -- and i am still driving it daily!

Jeny8675309ca 5 months ago

I have a 2004 maxima. I want to set it on fire. I had transmission problems, but will keep quiet about it lest I jinx myself. Anyway, problem is the check engine light. The codes coming up are for oxygen sensors. I've had them all replaced with some running over %100 and the light still comes on, same codes. Mechanics had it four times, told me to take it to the dealer. Dealer had it about 8 times, actually wiped the computer and reprogrammed it from scratch, light still came on, same codes. It's been almost 2 yrs now, the longest it stayed off was a week when they wiped the computer. I had them do a "hard reset" to get the emissions done and the light stayed off for 200kms. Ok truthfully, I've had the light shut off and come back on so many times that I know it comes back on in 211kms exactly, sad I know. The dealer couldn't figure it out so they came up with a story about having an after market exhaust, and it 1/16th of an inch smaller so it's reading it wrong...blah, blah, need a new exhaust for $2500.00, even thought mine was 6 months old at the time. The guys that did the emissions said the codes had nothing to do with the exhaust, it's about the mixture, it's running too lean or something. At this point I feel like taking a screw driver and poking the f**king light out myself. My gas cap is fine, you can hear the pressure release when you open it so I know its working. I've had so many problems with this car, it blows headlights at the drop of a hat, at $100.00 a bulb thats a pain. At this point if I can just get the damn engine light to stay off, I may consider not setting said car on fire.

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