Introduction: How to Fix Your Check Engine Light.

Picture of How to Fix Your Check Engine Light.

Fixing your car doesn't have to be expensive. Thanks to the age of information, anyone can be a "Google Mechanic". While this specific repair may not match your situation, it's the same process. So let's get rid of that annoying orange light.

A word of caution: if you have little or zero experience working on cars or using tools don't do this alone. Find someone who can work along side you to help prevent accidental injury or damage.

Step 1: ​Buy an OBD Reader.

Picture of ​Buy an OBD Reader.

Really, it's worth it. OBD stands for on board diagnostic. A reader will cost you about $60.00. You can buy one at auto parts stores or even Walmart. It may sound like a lot, but keep in mind, just pulling your car into a mechanic's shop will cost you a minimum of $75.00. That's just to look at it. At least this way you'll always have it and you can help your family and friends later.

Here's the basic principle of how OBD works. Your car has a computer which receives input from different automotive systems. When these systems send the wrong input (something is broken) the computer records the problem and turns the service light on. Plugging in the reader displays the code/s the computer recorded. These codes are generic diagnostic codes and not specific to a model (yes, there are exceptions).

We'll go over how exactly how to use a reader in a later step.

Step 2: Scan for Codes.

Picture of Scan for Codes.

It helps if you've paid attention to your car's performance prior to this point. If your vehicle has an emissions problem you may not notice any change in performance. Or, on the other extreme, your car may not even start. Being aware of what symptoms your vehicle has will help you pinpoint the problem. In my case my SUV was having a hard time starting especially after filling the gas tank. This was intermittent for about a month.

Look under the lower edge of your drivers side dash board. You'll find a trapezoid shaped port for the reader. Plug in the reader while the engine and ignition are off. Once connected, turn the key on but leave the engine off (KOEO). Press the scan button and watch the the reader think. It will eventually display codes stored within the computer. Scroll though the codes and write them down. In my case the code is P0496.

Step 3: Search Your Code.

Picture of Search Your Code.

So you have a code, now what? The internet is filled with all kinds of forums and threads. Often the code your vehicle has is a common occurrence with your vehicle. You'll find people have fixed it and written about it. A great website is It will give you a good understanding of what your code/s mean. If your know a thing or two about cars then this will help. If you don't, don't worry. Yes, it helps to know how something works before you fix it but you can get by here.

Search the code along with your vehicle. So here's what I wrote in the search bar. "Buick rendezvous OBD P0496." You might also add your vehicle year but keep this in mind. Vehicle models change year to year but what's under the hood may stay the same for years. If your vehicle is a 2008 and and the post is for your model but 2005 the fix could be the same. I found a post which said it could be the purge valve based off of my symptoms and code.

Step 4: ​Locate the Part. Remove and Replace.

Picture of ​Locate the Part. Remove and Replace.

So now I suspect the purge valve but what is it? What's it look like? Where is it? All these questions have answers you can find by doing an internet search. I found this diagram showing the purge valve. I compared it under the hood and located the part.

Once you know what the part looks like you can order it with confidence. I bought mine at autozone and replaced it in 10 minutes. It was a matter of 1 bolt, 1 hose, 1 electrical connector, and $24.00.

Step 5: ​Erase the Code.

Picture of ​Erase the Code.

Now that the part is changed, plug the reader back in. Press and hold the erase button. When the screen changes press the button again to confirm. The code is gone now and your check engine light should be off. This is assuming you have no other codes.

Important: if you're fixing a problem to pass a smog check, drive your vehicle for a day before taking it for testing. The technician can tell if you recently (within 50 miles or so) deleted the code. He will collect his $24.95 and tell you to come back again. If your check engine light is on when you show up, it's also an automatic paid fail. So make sure it's off before inspection.


steveburtis (author)2016-12-30

burtis I have a 93 Subaru loyale with a check engine lite on and can not find the geen connectors under dash to check codes? does 93 have them?

JohnF325 (author)2016-07-06

I have a 1998 dodge grand caravan and the check egine light comes on it will run but i have to keep my foot on gas and my oil smiles like gas i need help please

keldredge (author)2015-10-26

I love people that try to fix their own cars. After $$$ they bring it in to me to get it FIXED. :)

bob6715 (author)keldredge2016-05-15

so what do you to help your fellow man?????

tk42967 (author)keldredge2015-10-26

What I really love is when my friends bring their cars by after they've been to the shop and spent money to have a problem not fixed. Then it turns out to be a cracked vacuum line.

All because the "professional" mechanic just plugged a scanner in and started firing the parts cannon, rather than actually diagonosing the issue.

StevenR36 (author)tk429672015-10-27

Thank you sir or ma'am. keldredge, you
may very well be and likely are an honest mechanic inferring a well
intentioned point in your comment. However, Tk42967 is
making a valuable point as well.

I've personally lost count of
how many BS "fixes" I've payed for or been "prescribed". I once went in
needing only a new drum and rotor (or w/e, you know what I mean) to be
told I needed a new $800 axle (AND that I may as well throw in a trans
rebuild for several grand because "I'll need it soon"). The car was
"used" in the most extreme since of the term. I payed less than the
price of the recommended "repairs" for it, by far. That's the most
extreme example on the list, but it's a LONG list.

If I (as the "layiest" of laymen) have any advice to add to that of the 2 former's smart advice it's this:

you do find a trustworthy mechanic, treasure them like gold because they
are quite literally MONEY IN THE BANK! Short of that though, try to go
in with as much knowledge as possible (e.g. - an OBD), and the first
whiff of BS - about face and double time it because as soon as they get
their hand in your pocket it won't come out until you owe them those
pants along with everything else you have, er HAD
rather! Oh yeah, and your car will probably be 7 more different kinds of f'd up than when you walked in.

P.S I realize I speak anecdotally here but I know I'm not the only one either. If 1,000,000 chicken littles show up squawking - seek shelter!

MS71 (author)StevenR362016-04-19

Very well said and I agree whole heartedly.

nwonharp (author)tk429672015-10-27

see my other posts !

Cheers !

agulesin (author)tk429672015-10-27

Been there, seen that... Our Meriva had misfiring/stopping dead problems. Two "official" services and thousands of dollars later we found an "ex service" mechanic who diagnosed and fixed the problem within a couple of days. Since then we've taken the car to him. Good workmen deserve their wages.

dsearfoss (author)keldredge2015-10-26

you "sound" like a nice guy

enewbold (author)dsearfoss2015-10-26

Yep, a very "nice" kind of person who takes joy out of others problems.

dsearfoss (author)enewbold2015-10-26

Thought you would take the pain out of the problem

keldredge (author)enewbold2015-10-26

The truth hurts, but facts are facts. It was my job to fix them, and earn an income.

WildB (author)keldredge2015-10-26

I like smug people. It's all the more enjoyable when life reminds them that they aren't perfect and it wipes that smug smile off their face.

bob6715 (author)2016-05-15

I SEE you have been thru the ringer, as so many people have let me no the state you live in im in nc



rickfazz (author)2015-10-31

After 30+ years of being a mechanic mostly doing smogs and driveablity. Code scanner will only tell you what system is out of range. As time has gone on they have gotten more complicated. Most models have pattern failures meaning they often have the same problem. Due to part or system weakness or failure. If you think you know what the problem is and do the repair your self and the same code comes back it's time to stop wasting money and take it to some one trained too. A local school repair training shop my be a good idea.

AnubisAndIsis (author)2015-10-31

Two things:

- Don't overcomplicate things. If your car/truck/interstellar space craft is fairly new or you have little reason to suspect it requires service, stop the car, remove and replace the gas cap making sure it's threaded in properly and sealed, then drive the car for 10-20 miles. Often the light will go out on its own. I know, it's the most dumb thing ever to associate with an "Engine Service Soon," but it's really easy to do with newer gas caps (slightly cross-thread or misinterpret the cap is closed.) The OBD codes for a leaky gas cap are misleading and this happens a LOT, especially if you've recently gotten gas.

- Make sure your car/truck/interstellar space craft **is** an OBD II. Older vehicles will be OBD I and they are not interchangeable. Our 98 Cabrio is an OBD I and this scanner is an invaluable tool in the arsenal in keeping it running clean and lean.

Correction: It was my Toyota pickup that was OBD I, the Cabrio is indeed OBD II. Sucks getting old. :-P

g8aso (author)2015-10-31

I have had one of these for ages and it cost me more like $20.00 on eBay. It scans the error codes and asks Erase Yes/No.

Job done in 28 seconds.

AeonOne (author)2015-10-31

One thing I have not seen mentioned in the comments is ABS codes or airbag codes. Most of your cheaper OBDII scanners will only read the engine codes. Engine light is an indicator for multiple vehicles systems but not ABS or airbag. These systems have separate modules which take a more pricey scanner to read. If you are being charged $75 dollars for a shop to read your codes you're being robbed. Most auto part stores will read the code for you for free. We do not charge to read codes at my shop. In fact you're not charged unless we find and fix the problem. There are plenty of shops in the industry that give people like myself a bad name. I got into automotive repair because I'm good with my hands and I wanted to help people. It's not for the money. Mechanics make a starving wage. Most of the money you are forking out does not even see the mechanic. Keep that in mind when you go to pay your bill.

sking0369 (author)2015-10-25

The P0496 is really a foolproof code. Evap flow during non-purge. Of all the P0496's I've seen in the shop it has always been a bad purge solenoid. But what about some other codes? A P0300 is a missfire code and some testers may tell you what cylinder but then why is it missing? Spark plug or ignition coil, bad injector, low compression or even wiring to any of these components could be at fault? What component would you put on for a P0102 MAF performance code? Quite often this code is a vacuum leak. Money wasted if you'd go out and buy a MAF sensor.

AeonOne (author)sking03692015-10-31

P0300 is a random misfire code.. Normally meaning multiple cylinder misfire, If it was something like a P0301 or P0304 it would indicate which cylinder is misfiring. So P0304 would be a cylinder 4 misfire. But like you said you then must determine the cause of the misfire. Just adding to what you've said.

antagonizer (author)2015-10-31

The diagnostic tool is always good advice. I bought mine years ago when my mechanic wanted to charge me $100 just to plug it in. Since then, I've had my engine light come on over a dozen times and of those dozen times, it's been a sensor problem. Except for once where it was a loose fitting gas cap. What I'm suggesting is, always check your sensors first. For people that talk of expensive rebuilds, it can often boil down to something as small as a bad co2, brake, or pressure sensor.

nwonharp (author)2015-10-27

Here is the code scanner that I have . A Cen-Tech 60794 . I got it for $ 99.00 at Harbor Freight

Here is a couple of videos I found on how to use it , Thanks to North Carolina Prepper :

Cheers , take care and have a good day !!


nwonharp (author)2015-10-27

Yeah , like tk42967 said , Years ago , I had a Mercury Sable ( it was made before OBDII ) . there was a recall for some mechanical problem , and would be fixed for free . I took it to the dealership , and since it was running slightly rough , ( no " check engine " light ) , I asked them to check it over while they had in their shop anyway , and see what I might need to " tune it up " . They scanned it , and told me that i needed a " throttle position sensor " ?? and charged me $50 for the scan . I got one , and to get to the TPS to change it , I had to remove the distributor cap . I then saw the problem , the cap was shot , and the sensor I got was the wrong one , and didn't fit so I didn't replace it . I replaced the cap and rotary button , and it ran fine , no problems ! I called the dealership and they said that the computer codes don't lie and that I needed to replace the TPS , even though I told him that the cap and button solved the problem ! I asked him if his mechanics strictly rely on codes , and were afraid to get their hands dirty with other troubleshooting . I think I pissed him off ! I drove that car for years after that with no troubles at all , never did replace the TPS . I now have a Cen-Tech OBDII scanner for newer cars .

Cheers , take care , and have a good day !

leemck (author)2015-10-26

There is a car manufacturer industry wide policy of hiding and burying the theory of operation and technical details of how each specific model of car implements smog and emission control systems. This Instructable is right: Go to the web because consumer shop manuals don't have the detail you need. It takes reading quite a few web posts to get the details correct. I wasted hundreds of dollars fixing my daughter's Toyota because the vacuum egr switching valve turned off when the computer turned the valve on. The vacuum gage said "no flow" and I didn't realize it meant a hose was pinched closed. Duh~! I couldn't understand what the vacuum gage said because I assumed the valve worked "the normal way". -- After you struggle teasing out the hidden information that makes troubleshooting easy... be sure to complain. It is a cheat to sell a complicated car and then refuse to clearly describe how it works. I am a home mechanic with 52 years experience: The cars are honest and if I had about 3x more information they would be one third less aggravating to repair.

Doc_Cottom (author)2015-10-26

Always check your gas cap, it is responsible for many codes. It has to on tight.

PatrickP10 (author)2015-10-26

Good job,

I am not always negative, bad apple can destroy a lot of apples, but a good apple is always a good example for customers.

Altoidian (author)2015-10-25

A great Instructable..simple and to the point. I agree. You really do not have to be a mechanic to save bucks on fixing your car. Sometimes, if you know the problem before going to the mechanic, you have a distinct advanatage in negotiating the fix. Also, many fizes on modern cars are as simple as the one you describe. In my case, taking my Chevy in for a $24.00 item would have cost me at least $125.00 (minimum shop charge) plus parts; $149.00. Every car should come equipped with that OBD reader permanently connected and easily displayed. Why not is a mystery to me.

CraigRJess (author)Altoidian2015-10-25

Every car also should be equipped with cell phone jammers too, while the car is "running". Would solve a lot of the stupidity I see out there regarding phones & driving.

ac-dc (author)CraigRJess2015-10-25

No. There are legitimate uses for a cell phone while driving, like if you become the victim of road rage and it is not safe to pull over to make a phone call. Further, it is illegal to jam phone calls so automakers are prohibited from doing it.

Further, you can't mitigate range on such a device, it would inherently block the cell signals of a car next to you while you pull up to do an armed robbery. Further, many hands-off cellphone links to automobiles (integrated into the vehicle console system) are reasonably safe because it's driven by voice commands, no taking your eyes off the road to navigate a menu or especially not to text.

What we need instead is a responsible police force that tickets every legal violation, instead of trivializing some as not important enough for them to bother with, and more serious penalties for texting while driving.

sanmarr (author)ac-dc2015-10-26

How about a competency test given to new drivers to see if they have enough RAM to drive while talking or texting? Some people can do it, some people can't. Why should anyone else be punished by another's inability to give the attention safe driving requires?

KayjayUK (author)sanmarr2015-10-26

What an irresponsible comment.NOBODY is able to safely give attention to the road when their attention is elsewhere. There was a TV campaign here in England where they played two sentences being spoken at the same time, it was totally impossible to decipher either sentence. The law here should be extended to ban drivers from making calls even with hands free systems, you cannot safely talk and drive at the same time and this includes talking to a passenger.

kbowman (author)ac-dc2015-10-25

Plus what if the pizza guy is trying to find your house because you can never remember to turn the light on for him!!?

Yamelk22 (author)CraigRJess2015-10-26

let me correct you: every car should be equipped with responsible drivers who pay attention to the road instead of their phones.

dont need to thank me dude. bye

tk42967 (author)CraigRJess2015-10-26

So if I am the passenger in a vehicle, my cell phone should be jammed?

mattcintosh (author)CraigRJess2015-10-25

So the passenger isn't allowed to use the phone?

Altoidian (author)mattcintosh2015-10-25

With modern cars, you would think they might be able to build a sensor that could detect who is using a phone..which location has the most signal, etc. Heck, I think if I broke out my old radio books, I could build that.

The device that would blow the safety stats up would be an alochol detector...When I have ridden with drunks ( as the dd and my Dad was a drunk driver constantly!) you can smell the alcohol and it is very strong. If a kid can detect it, so should a computer. It senses a driver and passenger and at least one of them is toasted, a hint of alcohol fumes it shuts down ignition. As for taking drunks home..Nope! In my book, even that is unsafe. I've had too many uncontrollable drunks in my car as designated driver (I do not drink) But, enjoed an "outing" now and then (especially during football season), so in those days, I was always the DD.

mattcintosh (author)Altoidian2015-10-25

There was an article about that, and it said the problem was the reliability with them. Lets say the standard was the "6 9's". In computer terms, that means that you could boot up the server on Jan 1st, and by dec 31st, it was "down" for less than 32 seconds.

Lets say 119 million people drive to work in a given day in the USA. At 99.9999% reliability, 119 people a day have to call into work and say they couldn't make it in because the device gave a false positive. or by the end of the year, 43,435 excuses. But is any device going to be that reliable? How about after 5 or 10 years? Lets say the average person starts their car 6 times a day. That over 260 Billion starts in a year

mc2517 (author)2015-10-26

If the car is performing normally, ignore the light would be my option. If the light bothers you, cover it with grease pencil/china marker scratch. If something is really needing to be fixed, the light will be flashing and/or the engine will be limping.

tk42967 (author)2015-10-26

$5 for a smartphone app (torque is my preference) and under $20 for a bluetooth OBDII adapter. Sync the adapter to your phone and go. It may not be mechanic grade, but it will give you an idea and with alittle googling, you can find what you need.

Syncubus (author)tk429672015-10-26

Agreed. I prefer the Bluetooth adapter and software. I bought a standalone one, recently, for my less technical father (~$20 on Amazon for a 'budget' model).

PhillipJ4 (author)2015-10-26

I bought the more complete one that tells me what the code is. It has saved me and my family thousands of $$$$. You do need to be a little save about how a car works. I also save money by buying new part online. Last code was P0506, Idle air control valve. Dealer $148.00 parts store $85.00 online $43.00. I also clear the code once and see if it comes back before replacing parts. In the last case cleaned the throttle body of carbon.

johndavidf (author)2015-10-26

Find a retired Class A mechanic and have him change the part in his or your garage for much less money. Most keep their license's paid up for a number of years after retirement. Also gives a senior cash money when they need it. Why not pay $25 and hour rather than $90/hr. Most retired mechanics have all the right tools.

enewbold (author)johndavidf2015-10-26

Excellent suggestion. Hold down costs AND support your local seniors. Love it.

KevinM75 (author)2015-10-26

I bought an OBD reader after taking my car to a mechanic to see why the check engine light came on, leaving it there all day, finding alternative transportation and paying $50, I found my gas cap was loose. It's saved many $ since.

dsearfoss (author)2015-10-26

I have this one currently $30 US .. hooks to PC(laptop) via USB but can also record data , strip charts virtual dashboard and more they also have Bluetooth ,WIFI and other models the one at the Auto store cost more with less

Billster36 (author)2015-10-25

Remember, check the simple stuff first! I had a customer come in for a code scan that said Cam Phaser, V V T, and a few other things. Guess what? She was two quarts low on oil and the variable valve timing system didn't like it.

Ajax4Hire (author)2015-10-25

Much less expensive solution:

Buy an ELM-327 ODB-to-Bluetooth module.

This connects to your car ODB port. Use an SmartPhone App (I use Torque) to read the ODB port. Monitor 100s of measurements. Read, interpret and clear Engine Codes.

ELM-327 from Aliexpress is $6, from Amazon a little more.

kithmo (author)2015-10-25

No need to buy an OBD reader, buy a $4 bluetooth OBD connector and download an engine fault reader app on to your phone.

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