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

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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 about 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 be fixed by the car's owner.

The "service engine soon" light could just indicate a faulty gas cap.

The "service engine soon" light could just indicate a faulty gas cap.

What Is the Purpose of the "Service Engine Soon" Light?

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. Your 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.

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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?

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: My "Service Engine Soon" light stays on. What should I do to fix this?

Answer: If you are not capable of handling it yourself, or feel you do not know enough about cars, then you should definitely seek the help of a qualified technician.

Otherwise, follow some of the advice in the article to the best of your ability, again get professional help if it gets too difficult.

Question: My car shakes and the service light is on, what could be causing this?

Answer: Your car has a serious problem!

I can not fully diagnose here, but it sounds like a misfiring cylinder. That would cause the engine to run very rough.

Get to a garage/qualified mechanic as soon as possible.

It may be as simple as just needing new spark plugs, or it could be something much more serious.

Your mechanic will have the correct tools and knowledge to fix the problem.

Question: Why does the tire pressure light blink?

Answer: I think it may mean that the battery for the pressure sensor is low. Another possibility is that the pressure gauge is damaged or malfunctioning.

© 2012 Ardot

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