Check Engine Light On? Get it Diagnosed Free

by Ryan Guina

Last week I was driving to my fantasy football draft when my check engine light came on. “Great,” I thought. “Now what?”

It’s not a good idea to drive too far with your check engine light on because you don’t know what may be wrong. Unfortunately, a check engine light doesn’t tell you anything specific, only that your vehicle’s computer recorded a malfunction in the engine or emissions systems. Until you get the problem diagnosed with a scan tool, you don’t know what that problem is.

What to do when your check engine light comes on

Check Engine Light Diagnosis

Get a free check engine light diagnosis

Get the problem diagnosed ASAP. You wouldn’t drive far if your oil light came on because your engine could seize. Likewise, you wouldn’t want to drive far after your check engine light came on because it could be something equally disastrous (or it could be relatively benign). The point is, you just don’t know, and that can be dangerous.

Where to get your check engine light diagnosed

You have a few options to get your check engine light diagnosed. You can take it to the dealer or an auto mechanic shop, to an auto parts store like AutoZone, or you can check it yourself with a scan tool.

Dealer or auto mechanic shop. We’ll start with this option because these are locations where you can get your vehicle repaired. However, be aware of any associated costs before you get your check engine light diagnosed. Some places may charge a diagnostic fee, which they may then waive if you get your vehicle repaired at their shop. The advantage of getting your check engine light diagnosed at one of these locations is they can give you an in-depth diagnoses, repair estimate, and tell you potential problems if left unchecked. They may also be able to repair the problem that day, or schedule a time if the problem is not critical.

Auto parts store. AutoZone is well known for doing free check engine light diagnostics. Just go into the store and ask someone behind the counter. The process only takes a couple minutes and they will provide you with a print out listing the troubleshooting code and diagnosis, a definition and explanation of the potential problem, and probable causes. Keep in mind, this is all done from a computer and is not comprehensive! This is only meant to give you an idea of what the problem may be and will help you narrow down the troubleshooting process. Also be aware that AutoZone is in the business of selling parts, not repairing cars, and while many of their staff are knowledgeable, they may not diagnose the problem correctly on the first try. Before buying parts on their recommendation, do some research into the problem and try to eliminate some possibilities.

Diagnose the check engine light yourself. Diagnosing a check engine light with a scan tool is easy to do. Jut plug in the tool, turn on your car, and read the fault codes. The tools are inexpensive as well, starting at around $60, and going up to several hundred dollars. You can also reset the check engine light with a scan tool and see if the light comes on again (but do this at your own risk).

Which is better – dealer/auto mechanic shop, parts store, or DIY?

There are pros and cons to each. The dealer and auto mechanic shop should have certified auto mechanics running the diagnostic, so you should have more confidence that they will diagnose the problem correctly. However, there may be an associated charge. With an auto parts store or DIY, you should get a good idea of what system caused the check engine light, but you won’t get a definitive diagnosis or necessarily know how to repair the malfunction.

If you are looking for the frugal way to handle this, I recommend dropping by AutoZone or another parts store that offers a free check engine light diagnostic and have them run a quick scan. It only takes about 5 minutes and should give you a good idea of whether or not you can drive your car until you can find a convenient time to repair the malfunction, or whether the problem could be serious and requires immediate attention. If you have several cars, or an older car, you may consider buying a scan tool. At $60, you wouldn’t be spending a lot of money, and it could help you deal with an unscrupulous mechanic who may try to pull one over on you by misrepresenting the problem with your car.

What happened with my car? Well, there was an Auto Zone on the way to my friend’s house, so I stopped by and asked them to take a look. The problem wasn’t one that needed to be repaired immediately, so I got the troubleshooting ticket from them and went on my way. I bought a new car just under 3 years ago, and since it is under 36 months old and has fewer than 36,000 miles, the warranty should cover the repairs. So I will make a date with my local dealership when I buy new tires and let them take care of the repair.

Question for the readers. Does anyone know of any auto parts stores other than AutoZone that offer a free check engine light diagnostic? The only place I have ever gone is AutoZone (because they were the only auto parts store I knew did this and the locations were convenient). Thanks!

photo credit: angel_srt24.

Published or updated August 26, 2016.
Print or e-mail this article:

{ 49 comments… read them below or add one }

1 Ryan

Ouch! I’m sorry to hear it cost so much, Natalie! Keep in mind though, that the mechanics may have had to do more extensive troubleshooting than just reading the fault codes from the scan tool. The scan tool is a great tool to narrow down the troubleshooting, but it isn’t comprehensive. The fault tool results probably sent the mechanic in the right direction, but they most likely had to do more work from there. They charge high hourly rates, so that’s probably where they got you.

Thanks for sharing!


2 NatalieMac

Knowing this could really save a lot of money. My check engine light came on a couple months ago, and the dealer’s fee for diagnosing the issue was $220 which was above and beyond the repair fee, even if the repair was done there.


3 Dividend Growth Investor

This happened to me last year and I went to Good Year Firestone to get my car diagnosed and fixed. They did charge $99 fee + $500 for repairs.
Two days later my car stopped working on a busy intersection on my way to work. I towed it to the Firestone place that had supposedly fixed the car in the first place and they wanted to charge me $100 more for diagnostics.
They refused to admit fault and informed me that sth else was broken, which will cost another $500..Apparently whenever they run a diagnostic and then whenever the mechanic performs their manual check they fail to see stuff that’s not working..
I finally went to a mechanic that I know and he fixed my car for $180. And it’s still working. The problem seems to be the same as what GY told me the problem was..

Of course my honest opinion is that you should bring your car for repairs to small mechanics who happen to be family friends or very close to your friends. The big time autoshops are in the business of selling stuff and their incentive is not to fix your car but to get as much revenues as possible from you.

As a result Good Year Firestone lost a customer and I have been pretty vocal about telling people NOT to go there.


4 Doug

I wish I would have read this. I went to Firestone a month ago to get my check engine light diagnosed so that I can renew my CA registration. They kept it for the weekend then told me Sunday night they couldn’t diagnose it because their good technician wasn’t there. They had charged me the $99 so they told me to bring it back. I brought it back and left it there the following weekend. They couldn’t get to it Saturday and late Sunday they told me it would take $850 to fix 2 “upstream air/fuel sensors”. I brought it back the following weekend and they did the fix. They reset the system and I had to drive it for another week to get enough data to pass smog. I took it to a smog only shop (California is just impossible) and just as I was arriving the check engine light came back on, so they wouldn’t smog test it. I immediately brought it back to Firestone and they said they were too busy to look at it for a few days. Considering they have charged me for something I didn’t get you would think they would care enough to jump on it right away. Now I am late to register and California is increasing my registration fee. If I get pulled over I have all the receipts to show I am doing my due diligence to comply with the law. I don’t know whether to hate California or Firestone more, but they definitely know how to play off each other to screw me. I don’t know what else to do.


5 Sara

I believe I have used Advance Auto Parts (AKA Discount Auto Parts in the south) to run a diagnostic on my car.


6 Ryan

Thanks for sharing Sarah! I think there is an Advance Auto Parts down the road from me. I’ll check them out next time if they are closer than AutoZone. ๐Ÿ™‚


7 Steward @ My Family's Money

I have found that check engine lights could be way more informative. I once borrowed my friends car and almost had a conniption fit when I saw the “check engine” light on halfway through a drive. I though, “What the heck have I done, the sky is falling.” After pulling over at the nearest gas station I had my wife ring my friend on the cell phone contraption that she carries to inquire about this apparent mechanical malfunction. I was pleasantly surprised that in my friends car the light is always on and that it doesn’t mean anything.

I wish that they had different color lights or something for the severity of the problem. Green is “not bad at all, keep driving,” yellow is “this is getting serious, take it to a mechanic asap,” and red would be “pull over now or you will die in a burning conflagration of doom and aluminum alloy.” That would be way more helpful.


8 Andrew

Actually if the light is on solid you are likely ok to keep driving, if it is blinking shut that sucker down asap and have it take to a shop.


9 Jarhead

Sometimes you can fix the problem yourself very easily. My light came on a few weeks ago after a long road trip. I looked at the mileage and realized that I had been a little bit late on changing my air filter. Now as most of you know changing an air filter can be done in about 4 seconds flat once you go to Wally World and get one. Once I changed it I started the car up and the light was off. So if you know you have been lacking in your preventative maintenance catching up on it might be all it takes.

PS Also ensure your fuel cap is on tightly as this can trip your light especially in newer cars


10 Ryan


I agree, I wish there was something a little more definitive that went along with the light because there really is no way to tell what it is.

Jarhead, great tips. ๐Ÿ™‚


11 RC@Thinkyourwaytowealth

I had a similar situation, several years ago, where the dealership charged my $75 to diagnosis the problem, then wanted $500 to change the spark plugs, wires, and ignition coil.(It was under warranty but spark plugs were not covered) I kindly told them no, spent about $40 on a scan tool on sale at pepboys, and proceeded to replace the plugs and wires for about $50 in parts. There are many online sites that explain what the codes mean (or what could be causing them). I had used autozone a couple of times before that as well. Some mechanics, but especially the chain places or dealerships, totally rip you off on the “diagnosis” fee.


12 tiffanie

Very good thing to get it checked ASAP. I had an older car that the check engine light stayed lit ALL the time, which was annoying. (I had it checked, and they couldn’t figure out why. Basically was just a wiring issue.) Great info, thanks ๐Ÿ™‚


13 Ryan

RC: yeah, I recommend doing it yourself first by either going to a parts store to have a free diagnosis done, or by buying a scan tool. That way you at least have an idea of what the problem is. If the repair is beyond the scope of your abilities, then you at least have a starting point when you take to a repair facility.


14 Ryan

Tiffanie: If my vehicle’s check engine light constantly came on, I think I would buy a scan tool. That way I could monitor the fault codes for any changes, and reset anything that wasn’t serious (that way I don’t become immune to the light being on and miss a potentially serious problem). I haven’t had the need to buy a scan tool yet though, because this is the first time the light has come on in the 3 years I’ve owned this car.


15 Alisa

My check engine light came on about a year ago, and in all honesty, with a super hectic life I kind of blew it off a little because the car was running fine.


Thankfully, everythink was ok when I took it in for a check, but when I realize the damage I could have caused by driving and not knowing if there was a serious problem or not; I start to cringe.

Thank you for sharing places that we can go to get it diagnosed!

Be well.


16 Darin

Checker Auto also does free diagnostics.


17 Merna

My check engine light went on the day before your post, so this was very timely. My husband took the car to Autozone as you suggested and they said they no longer provide this service. He said something about California law changing in the past two months and they no longer do it.

So the car is in the shop. Who knows what’s wrong? We’ll soon find out.


18 Ryan

Merna: This must be something new to CA, and have to do with liability reasons. I went to AutoZone 2 weeks ago (in OH) and had my check enging light diagnosed for free. Since you would have to take your car in for potentially expensive diagnostics, I recommend buying a scan tool. Inexpensive scan tools cost around $60, and better tools can be had for around $100. You would easily save that much on your first diagnostic test. Even if the repair is out of the scope of your abilities, you have an idea of the problem and can use that info to help you determine if unnecessary repairs are being made.


19 RON



20 sail

That’s correct. Pepboys will do the check engine light diagnosis for free if you enroll for their rewards membership, which is also free.


21 Colvini

Just called PepBoys here in Waldorf, MD and they wanted a $97 dollar fee for check engine light, must differ per state.


22 Sunil N

All they do for free is the evaluation – pulling up the codes and not a diagnosis.


23 Vic

Hello, to all

My name is Victor and I am a Master Certified BMW Level 1 Technician in the Houston area. I was reading all of your comments and would like to take this opportunity to ask all of you a question so that I can better serve my customers in the subject of diagnosing CHECK ENGINE LIGHTS. I have worked on many different makes and models, I have over 1600 hrs of class room training in general mechanics and diagnosis also over 1200 hrs in BMW specialized training, so I am very confident with my diagnosing skills.

I noticed that most if not all of your concerns had to do with getting ripped off or having to buy unnecessary parts. I recently purchased a diagnosing scan tool from Matco Tools to help me diagnose non European vehicles such as (GM, Ford, Chrysler ect.) The scan tool that I purchased is Professional scan tool that cost no where near the $60 or $100 dollar scanners for the consumers which I believe are worth every penny.

As a professional technician I believe that charging a fee for diagnosing a vehicle is fair and I also believe in fixing it right the first time. How would you feel as a consumer if I as a professional charged you a neutral fee such as lets say $80.00 for diagnosing a check engine light but instead of your regular diagnosis, what if I would Guarantee my diagnosis.

For example, Lets say you come in with a vehicle that has a check engine light, I diagnose it and determine that your electric throttle body is at fault. You decide that you could change the throttle body yourself and save some money on labor cost. I could tell you with certainty that the throttle body is to blame. The guarantee would be if you purchase and install a throttle body and it does not fix your problem I will purchase back the part from you at your full cost. Would that give you the consumer more confidence and would you feel better about spending the $80.00 for the diagnosing.

Thank you, for your time any input would be greatly appreciated..


24 Ryan

Vic: A guarantee like that would be good for many consumers, myself included. But I would probably first try for a free diagnoses and if the test results were inconclusive, or the part was expensive or difficult to replace, I would then consider a guaranteed diagnoses for $80.00. But I would have to be able to do the labor myself in order to save money with the $80.00 diagnostic fee. Otherwise I would be spending money on the diagnostic fee + labor.


25 Tom

Good article! I just came back from Firestone, where my car is in for service (at this point, brakes and oilchange). My check-engine light came on a few days ago, so I asked if I could also get a tune-up (overdue) and if they could look into why it lights up. They told me there is a $99 fee to run a diagnostic on my engine. I said that I can’t really afford that right now, and they told me they will run the tool (but not do any manual checking) and tell me what the codes is. If a tune-up could take care of the issue, they will let me know. (of course, I suspect they will still ask for $99 to reset the light, in which case I may decline that particular portion and go to Autozone..)

I don’t really understand why the diagnostic/reset fee can’t be waived if the customer does necessary tune-up/repair at the facility. I do understand that they want money for a full diagnostic check if the customer decides to fix it somewhere else though.


26 Ryan

Tom, The diagnostic fee usually involves more than just using the scan tool to get the trouble code. It often involves a manual inspection or running specialized tests on their computers. So I understand the diagnostic fees. But just getting you a troubleshooting code is pretty easy, and anyone can do that with a scan tool.


27 Tom

Hi Ryan,

Quick response ๐Ÿ™‚

Sure, I see the difference between a full diagnosis and running the tool. I still think that if they get say $300 to fix the problem, it is unnecessary to charge me a $100 to find the problem they have me pay to fix though ๐Ÿ™‚

The guy at Firestone actually brought up the point about “Well to reset the light, we still have to do the $99 diagnostic” early on in the conversation.

I guess I’m a bit frustrated about how expensive it is to own a car – wish I lived so that I could ride a bike instead, haha.


28 Denny Pard

Iโ€™m sorry to hear about your situation. When I had that problem with my car, I found this e-book called The P.S. Lanard Automobile Troubleshooting Guide. My repairs ended up being a lot less than I thought. Hope everything works out for you.


29 Cody Kittell

Yea i have a ? . i have a 95 ford thunderbird lx and my engine light came on the other day and my car as been running fine4 since the day i got it and i still have no problems.. what should i do?


30 Ryan

you should get it checked out. It could be a problem, or it could just be a service light. But you won’t know until you have the fault code read.


31 Howard Herman

I think the thing that is missing here is to find a good mechanic. This is perhaps the most difficult but best way of saving on repairs. Find a good mechanic by speaking with friends and family. Most everyone has a car and at some point in time that car will need a repair. Word of mouth backed by experience is the best criteria I know. Once you establish a relationship usually certain fees (like diagnostics) will be waived because they know you will have them do the repair and that the next time something happens you will return to them. One other thing: there is a capital investment involved with purchasing diagnostic equipment and a mechanic has the right to recoup that investment. Finally, I am not a mechanic but have had good experiences and horror stories. The best advice I can give is to go find a mechanic that is competent for your make of vehicle.

There is a nationally syndicated radio show called “The Car Doctor.” His name is Ron Anainian and he owns a shop in norther New Jersey. He knows everything about anything that relates to a car. You can look him up on the web. He will take and respond to questions either on his show or via email. He is THE BEST because he will not only explain the cause of the problem but he will provide insight into how to get it repaired and what the cost might be so you have some insight.


32 santroRaj

My check engine light was on yesterday. I took my car to AutoZone to run the OBD. Got a code of P0456. Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could possibly cause this code as well or if the cap wasn’t properly tightened. The gas cap seal was adjusted and tightened properly and there was no check engine light. Thanks guys for the info.


33 Ulysses G. Smith

Had 97,000 mile check up on my Volvo. within 3 miles traveling home I notice the check engine lite came on. when back to the service place, & they will not reset this lite.


34 Ryan

That’s poor service on the part of your service department. I would contact their manager and inform them you won’t be giving them any future business.


35 Andre

Gooooooooooooooooooood my engine lights is on sucks bmw always something I should just drive my honda or toyota they never have problem like bmw


36 mary patrick

I ‘m glad to see the most fairly recent comment from santroRaj. I too took my car to auto zone to see what the codes were for the check engine light that came on my in car. I live in Escondido, CA. They told me that Govenor Schwarzenegger didn’t allow them to perform that service any longer. Do you know if this is true or not? Were they just pulling my leg?


37 Ryan

I don’t think the Governor cares whether or not they offer that service, I think he has more important things to worry about.


38 Jenni

No, they were correct. I just went in and was told the same thing. I called my dad to double check this information (he’s always up to date on these kinds of things) and he said that it is true.


39 Myself

I just went to autozone on San Pablo Avenue in San Pablo, CA to have them diagnose my Check Engine light and I was told they do not offer this service in the State of California, rather they could sell me the cheapest $60 auto error code reader, which I declined.


40 Scott

I went to AutoZone Simi Valley CA, they no longer will check your car with a scanner for the trouble code. They said “laws” were changed and they are no longer allowed to scan codes because they do not repair cars. I called Pep Boys and I was told they will scan for the code and reset the light. I went the next day and was told they would scan for the code but NOT reset the light unless they repair the car. I seem to get a different explanation with every phone call.


41 RN

I went to an Autozone in TX today and they still give a printout for free. The guy even told me what to do to fix it. I had washed the underside of my car earlier and he said I probably got water in the O2 sensor’s cable connection; just to unconnect and to blow dry.


42 Becky

Ok i have a diagnostic done on my car and I paid the $100 to get it. Now can I take that diagnostic report to different mechanics to get the best price for my repairs?


43 Ryan Guina

If you have a copy of the diagnostic you should be able to take it anywhere. Shopping around is a great way to save money. I would also check with the mechanic who performed the diagnostic to see if they will give you a credit toward any repairs equal to the amount you paid for the diagnostic. Many repair shops do this.


44 lawrence

Remove your battery cables for 20 minutes. Re-attach. Voila…no more check engine light.


45 Lorne

I found this article helpful. It talks about the 5 top reasons the check engine light comes on in the first place. Your article and reader comments have given me some options.


46 tammy

Went to auto zone in oregon and did a free diagnostic and came up with a code P0300. Going to dealer tomorrow and hopefully it wont cost alot to fix this light problem. It really sucks for people who are low income and have this problem. If I cant afford to fix it then I have no car. It cant be a gas cap because the light was on before I put gas in it.


47 Premie joseph

I have a 2010 Toyota Sienna. My check engine light, VSC light came on. I took it to autozone. Free check was done and possible causes 4th cylinder missfire, blocked fuel injector. Sold me Lucas fuel cleaner. However problem was not resolved. I took it to firestone, Monroe, LA and they charged me $104 for diagnostics and told that I need to replace spark plugs. ignition coil and have a fuel system cleaning with total of $800 with diagnostic fees.. I was not so sure that this was the problem and fortunately a friend advised to get my vehicle back. I took it to a friend’s mechanic and he discovered that fuel injector cord was chewed by a squirrel. He fixed my vehicle and engine light is off and running smoothly. Be careful ladies when you take a vehicle to Firestone. I would have paid for unnecessary services.


48 Don Pfeifer

Does your car have to be running when you scan check engine light


49 Kurtis

Advanced auto parts told me today they stopped diagnosing engine codes in April 2016. Too bad my light came on in May! I’m pretty sure what my problem is and spending 99.99 for a 15.00 part is stupid


Leave a Comment

Previous post:

Next post: