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Seeing any warning light on our vehicles can drive someone straight into panic mode. Here's how to stay calm and know exactly what to do if you see your check engine light turn on.

We recently bought a car for our kids to drive. It’s a beauty, too. We’re talking a 2004 Mercury Sable with 170,000 miles. And after just a few short weeks of ownership, the dreaded “check engine light” came on.

Now we did what most probably do–we took it to a repair shop. I learned a few things from the experience. One was never to go back to AAA Service Station (see below). Based on my costly experience, here’s what to do when your check engine light illuminates.

The Dreaded Light

First, lets talk about what the light actually means. The computer in your car that triggers the check engine light is monitoring the efficiency of your car and the emissions. When the light comes on, it doesn’t necessarily mean you have to stop the car immediately. But you do need to determine what the problem is as soon as possible. If the check engine light is on in conjunction with the low oil or high temperature light, however, there may be more serious problems with your car that should be addressed immediately.

In my experience, the check engine light usually indicates a small problem that needs to be addressed before it becomes a larger (and more expensive) problem. Continuous driving with the check engine light usually means you are experiencing reduced fuel mileage and reduced performance. The check engine light can indicate something as simple as a loose gas cap or something more sever such as a bad sensor or excessive exhaust. We see the light a lot on our Honda Odyssey, and every time it’s because we haven’t screwed the gas cap on tight enough.

So now that you know something is wrong, what do you do? You have a few options.

Go To A Mechanic

One option is to take it to a mechanic for a diagnostic test. A mechanic will plug your car to a meter that will give him a list of trouble codes that were logged when the check engine light came on. These codes will tell the mechanic what the problem is. Before you head out to a mechanic, however, there are a few things to consider.

First, before you even go to a mechanic, make sure you ask what the charge is for the diagnostic test. Second, if there is a charge, then ask if the fee is credited towards the repair bill. I assumed my diagnostic test fee would be credited towards the bill as long as I had them do the repairs. It turns out that AAA service shops don’t work that way. As a result, I paid $150 for diagnostic tests that took them about 10 minutes to complete.

Of course, I won’t be going back to an AAA shop. There are plenty of mechanics in my area that don’t charge anything for a simple diagnostic test. If mechanics near you do charge, make sure the fee is credited to the future cost of repairs. If not, go to a different mechanic.

Purchase A Diagnostic Tool

If you are more of a do-it-yourselfer, you can purchase a code reader online or in most auto parts stores. The reader works just like the diagnostic tool used by mechanics. You plug it into your car (usually located under the dash on the driver’s side) and it will retrieve the error codes. Some of the tools show you the error codes on their display and provide a book to translate the codes. Others require you to plug the tool into your PC and software will interpret the codes for you.

The code readers can range anywhere from $25 – $300 and can easily be found on Amazon. There is even an iPhone app called the goPoint Technology GL1 OBD-II Accessory for iPhone (also works with iPod and iPad) that can tell you why your check engine light is on. If you are able to do the repair work, a code reader can pay for itself quickly.

Visit An Auto Parts Store

Another option would be to take your vehicle to an auto parts store and have them plug in a code reader. Many stores provide this service for free in hopes that you will purchase the parts you need to make the repair. If the repair requires special tools, they will often rent those to you for a very small fee (and some will return the rental fee when you return the tool). Some stores are even able to give you directions or diagrams to help you complete the repair.

Author Bio

Total Articles: 1118
Rob founded the Dough Roller in 2007. A litigation attorney in the securities industry, he lives in Northern Virginia with his wife, their two teenagers, and the family mascot, a shih tzu named Sophie.

Article comments

Money Beagle says:

I never thought about going to an auto parts store but this makes a lot of sense. I just went there to get a battery tested last week, so why wouldn’t they have the same capabilities to read other important things as well? Thanks for the tip!

gypsygirl says:

When my check-engine light comes on, when I need a bulb replaced, etc., I go to an auto parts store. I purchased a battery from them in the northeast, then came to Florida three years later. My battery was not up to par. They diagnosed and found that my battery was bad and gave me a free battery, as I had purchased the previous one from the same chain. They never charge for anything except for the parts and they will install free of charge!

jim says:

I’ve done it at the auto parts store. The AutoZone location near me does the check for free. They were able to tell me that the problem was a broken oxygen sensor. It was quick and easy. I ended up going to a shop to have it fixed but at least this way I knew what was wrong and knew how urgent the problem was. O2 sensor isn’t a big deal generally I don’t think so I wasn’t worried about my engine blowing up or anything.

Emily says:

I would never assume it’s something small; would take it to mechanic immediately.

Larry Copling says:

@Emily: …which is exactly the position that predators at repair shops expect a woman to take! Please- don’t make emotional decisions concerning your automobile. Get the facts- as cheap as you can- then make the best PRACTICAL decision. It may not make the repair guy happy, but your pocketbook will become your best friend!

gypsygirl says:

I agree with Larry. Even when I had a diagnostic check done and it was for a catalytic converter, I then took it to a mechanic. The mechanic told me that most people would not do that and it was a smart thing to do!

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Ace says:

I work at an oil shop and we check check engine lights for free, most often if you can find somebody with an obd2 reader it will give you the engine code and the problem which you can then take the tart make model of your vehicle followed by the code number (2014 Toyota Highlander p0101) and get the information for what’s causing the engine code without spending a penny. My girlfriends car was throwing a code and it was an electronic throttle body re learn procedure and I YouTubed it fixed the problem and no more code. More often than not you’re going to pay out of pocket for any engine code that’s not really necessary.