By November 22, 200564 Comments Read More →

Check Engine Light – What Does It Mean?

Do You Really Know What That Check
Engine Light Means?

Reader Question: My
check engine
light came on the other day what should I do?
Will it hurt my car if I continue to drive it?

Dear concerned car

     I hear this line at least once a week. The instrument panel on
most cars is absolutely cluttered with warning indicator lights
and buzzers. These lights are color-coordinated so that different
colors indicate the severity of the potential problem. As you
start the car, all of the lights should come on, and as the
computer verifies each component is working properly, the light
is turned off. You should only be concerned with lights that
remain on for several minutes after the car has been started.
Check engine lights can be tricky to repair, so a little help on
your part could really save the mechanic some diagnostic time,
and save you some money!

Treat check engine light, and all dash lights like traffic
A Red
Warning light
indicates an immediate danger. Pull
over, turn off the car immediately and assess the problem.
Symptoms that usually cause red warning lights are engine
over-heating, low oil pressure, transmission over-heating, low
battery voltage, and brake failure.

Red lights can also indicate a safety issue, so proceed
with caution as you maneuver to stop the vehicle. Unfortunately,
when the red light is illuminated the problem is at its
It can be a matter of seconds before permanent engine
damage occurs.

Some common things to look for when a red light comes on

  • low anti-freeze, engine oil, and transmission fluid
  • low brake fluid
  • missing belts
  • faulty alternator that is not charging the battery or a bad

A Yellow Warning
(Usually a Service engine soon light) indicates
"Proceed with caution." The onboard computer system has
indicated a potential problem and is alerting the driver. This
computer system resets and re-tests all sensors and indicators
each time the car is started. The computer system is capable of
correcting some minor abnormalities, but if the light continues
to come on after multiple car starts, it is probably sensing
something that would imply a visit to the diagnostic mechanic is
in order.

Some common things that may cause a yellow light (Service
engine soon light) to come on, but will probably require an
experienced technician to diagnose are:

  • anti-lock brake systems
  • safety restraint systems, such as air bags
  • emissions components
  • computer-related problems, such as faulty sensors

If you are driving your car and a yellow light comes on, ask
yourself these questions:

1. Did you notice problems when starting the car? (slower to
start than normal..etc.)

2. Have you noticed a decrease in fuel mileage recently?

3. What is the over-all running condition of the car? Is the
engine misfiring or not performing like normal? Are there any new
noises from under the hood? Turn off the radio and listen closely
as you drive the car.

4. Do you notice any odors, such as a rotten egg smell, or see
visible smoke from the tail-pipe or from under the hood?

     Make sure to note the exact location and wording of the light
that has been coming on, because Murphy's Law dictates that
the light will suddenly not come on when you take it in to the
repair shop.

     In some cars, "engine" is the more serious red light,
whereas others use "check engine light," which is a
yellow caution light. If the mechanic thinks you are seeing a
yellow "check engine light," and your car is indicating
a red "engine" danger light, this could be a costly
mistake for both of you. Why? You could be having a serious over
heating problem and the mechanic is assuming you are having a
less serious caution light illuminating. The mechanic then might
give you the "green light" (no pun intended) to proceed
with your out of town road trip with the kids. Yikes!

Start the car, and point to the light
to ensure good communication of the problem.
dash warning lights can be a pain and hard to diagnose!
Diagnosing the problem in some cases will require the light to be
on while the mechanic performs the diagnostic test. If the light
is not on when you bring the car to the shop, you might be
wasting your time and the mechanic's.

a "running condition and dash light" log in your car to
help the mechanic pin point the root of the problem. I have a
customer who keeps such an accurate log of her cars'
complaints that sometimes I can diagnose the problem correctly
with the help of her log and by taking her along on my initial
test drive. I can do my diagnosis usually without opening the
hood to her car. This saves me time and she saves money on a
diagnostic charge. This customer can also hold me to my warranty
time period, because she had this particular complaint
written in her log book.

Submitted by a reader I just wanted to add something. Sometimes the check engine light is something simple…. In my car, 1990 BMW 535i…. my check engine light will come on if the gas cap is off, the oil cap off, dip stick left out or anything relating to emissions is out of wack. It was a huge relief one day when the light came off to realize the oil cap had been left off… and didn’t fall out of the car!

64 Comments on "Check Engine Light – What Does It Mean?"

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  1. Porscha says:

    I my ABS light and battery light as well as my check engine just came on. I noticed that whenever I stop I have to press hard on the gas in order to get the car to go. Once the car is going the battery light and ABS light go off. Any idea what it could be?

    • By Austin Davis says:

      Humm, if this is a GM vehicle I would check the alternator first, a problem with the alternator can cause all 3 of those lights to come on, although the alternator can continue to charge the battery so there could be no symptoms of a dead battery which you would expect to see if the alternator was bad. A simple electrical test of the alternator can help rule this out.

      Now, the part about having to press the gas harder than normal to get the vehicle moving….I’m not real sure what that is. If the RPM’s of the engine are slow to go up in relation to the amount of gas you are giving it could be a lack of fuel problem like a bad fuel pump. If the RPM’s go up rapidly in proportion to the amount of gas you are giving the engine but the vehicle is just not moving as fast as the engine is spinning I would assume there is a transmission slipping issue.

      I would suspect these two problems are related, so reading the computer codes with a scanner and doing some normal diagnostic testing is where I would start.

      Keep us posted, I am curious as to what is going on.

  2. lisa says:

    i left the oil cap off the other day and drove the vehicle all afternoon discovered later in the day put it back on but its running really rough and now check engine light is on.. any advice its a 1999 ford explorer

    • By Austin Davis says:

      I would expect the engine to run a little rough with the oil cap off since it will cause a vacuum leak. Re-installing the cap should bring things back to normal though. If there is still a problem with rough idle after cap is replaced I would look to see if there is oil on the spark plug wires or anywhere on the top of the engine with electrical wires. I would imagine that some engine oil has blown out of the engine and is causing an issue with some electrical devices.

  3. Anonymous says:

    It’s in reality a great and useful piece of information. I’m glad that you simply shared this helpful info with us. Please keep us up to date like this. Thanks for sharing.

  4. Sheila says:

    I have a 1998 Passat 1.8L turbo and the yellow check engine light, the abs light and the parking brake light are all on on my panel, I have checked the fluid levels and they are good, but I’m puzzled as to why all 3 of these lights would be on together, I would appreciate any help from anyone out there

    • Austin says:

      This is more than likely an ABS brake sensor failure or some kind of problem with the anti lock brakes. I would NOT suggest you drive this vehicle like this unless you are 100% certain things are safe to do so. Brake fluid loss would be the first thing I would look at, and check the brake fluid level inside the brake master cylinder. If the fluid is full, you will most likely need to get a mechanic to hook his computer up to the vehicle and “Read the trouble codes”. All 3 lights are on to really get your attention, there could be an unsafe issue with the brakes. The ABS system is probably disabled by your onboard computer until the problem is corrected. Take this seriously.

  5. Jimmy says:

    Thanks for the advice, yes the longest it has stayed on to date is only a few seconds, and it only seems to happen after more than 45 mins driving so I’m not too worried at present. Thanks again for the advice though, this is definitely the best thread I have come across on this topic. Cheers from New Zealand 🙂

  6. Jimmy says:

    Hey there, I get a yellow check engine light come on momentarily every now and then on long trips, usually when braking or coasting down a hill. If i tap the accelerator, the light disappears. Any ideas what could be going on here? Thanks.

    • Austin says:

      That’s pretty darn weird alright. I don’t think I would be too concerned about this though you might want to get the computer codes scanned now just so you know what codes are stored today and if any more codes show up later that might be more concerning. I would doubt that any codes stored today are worth pursuing just due to the labor costs involved in tracking and testing sensors and components. This is probably some kind of emissions sensor that is starting to fail and If I were you I would wait until the light stays on steady or some other problem arises before I decide to spend time and money on repairing it.

      Remember, if the light goes out the computer either saw the problem go away or it reset itself and the problem did not return so what ever it is it’s an intermittent issue and those are tricky to track down. IF the light is ON and you are close to your mechanic do NOT turn the engine off and let them check your computer codes while the light is on…that is the best way to get a positive ID on what is happening.

  7. Great article. So many people don’t know what to do when their check engine light comes on. They need articles like this to help them. Good job.

  8. samantha says:

    my check engine light came on and was making a puttering noise i check the oil and it was realy low

  9. James Torn says:

    A check engine light basically tells you that there is something wrong with the car. usually it is emission related like mass air flow etc… now and days, check light can basically tell you everything that is wrong with your car.

  10. Hope says:

    I have a 2004 toyota corolla. The check engine (yellow) light came on two days ago and was wondering what could be the cause? I just bought this car a week ago and am just a bit concerned. Any advise?

    • Austin says:

      Did you read my article? Most likely an emissions type of sensor is out of whack, although if the engine is missing or running badly something as simple as a bad spark plug could be the culprit of the missfire thus the check engine light. if light continues to come on, I would advise getting a mechanic to read your computer codes and go from there before you start guessing at things.

  11. alan says:

    my 2002 ford taurus with 65000 miles has a constant yellow engine warning light. 2 differect mechanics have read the computer but nothing is there. i unplugged the negativce battery post for 24 hrs. now i will do the positive only as suggested here. i read somewhere that the fuel filter might be at fault or an oxygen sensor or vacuum leak. but there is no repeat no computer code.

    • Austin says:

      There has to be a code stored in the computer memory…..unless you have a problem with the computer itself. Has you gotten a diagnosis from the dealership? I would do that. It is pretty rare to have to replace the computer itself but it’s also rare to not have a code stored.

  12. Alex says:

    Great article. Hit the major points, always remember to check the basics before heading to the dealer to spend a load of cash

  13. DM says:


    I recently bought a 1994 Buick Lesabre with 165K miles on it. Previous owner maintained it well and it runs great. I’ve been driving it for 3 weeks and the yellow “service engine soon” light occasionally comes on. But the thing is, it doesn’t come on every time. In fact, in the last 3 weeks, it has only come on twice. Both times though, when I turn the car off and restart, the light does not come back on. Since it only comes on intermittently, should I take it to a shop to get the codes checked? Or is it a waste of time at this point? Should I wait until the light comes on consistently?

    Thanks in advance!

    • Austin says:

      Personally I would wait until the light comes on and stays on more contantly or other symptoms occur like running poorly,poor fuel mileage or slow starts. I had a few customers with these vehicles and it did the same thing for years. If you have the money to spend, get the codes read, but I would be causious as to how much time and money I spend on trying to keep the light out. The best time to read the codes is when the light is on and the engine is still running. That might be difficult to produce at this stage. There will be codes stored, but how accurate or helpful those codes are will be the challenge.

  14. Th says:

    I live in Crane, TX. I was going back home for a Visit around Christmas in Indiana. Going through Oaklahoma I came to a gas station that had 86 Octane instead of 87 Octane like here and Indiana does. As far As I know of the car has always had 87 Octane or higher in it. I got the car in August of 2010 and I have always put 87 in it.

    I have a 1986 Delta 88 Royale Brougham with 3.8 V6 motor in it. It has 87,000 miles on it. Every since I put the 86 Octane in it in Oaklahoma the Yellow Check Engine light will come on but go out after I start driving again. They yellow or it looks orangish to me Check Engine Light will only come on when I start the car to warm it up and leave it idiling for a few minutes or if i stop and put it in park and leave it idiling for a few minutes…. Either way that it comes on when I start driving or driving again it will go out and stay out until I put it in park and it idles a minute or two again.

    I drove it all the way back from Indiana to Crane, TX and it ran fine all the way back. Am I hurting my Oldsmobile by driving it like this? I purposely look for the 86-90 Delta 88’s and 98’S and buy them. I really want to keep this car for a long time.

    Do I need to put gas treatment in the car or do I need to file a complaint on Oaklahoma for tearing up my car? Please help me out here. Thank you very much for your time.


    • Austin says:

      Not sure that small of a change in Octane would have an impact on the check engine light or not.I would rather suspect it was just coincidence. I would have someone read your onboard computer codes and see what codes are stored and try to clear and reset them. It is a 15 year old vehicle, and would not be shocked if the oxygen sensor is due for a change. Taking a very long freeway trip to Indiana could be the culprit of the light rather than the fuel rating.

      Hopefully its something simple and inexpensive but you are going to have to get a mechanic to hook up their computer to your vehicle to find out what it is.

  15. Dam says:

    On our Ford Focus, the yellow engine warning light comes on when we put lower 95 RON (standard) petrol in. Put in more expensive 97 RON fuel and it goes out immediately, 100% reliably.

    I’m assuming this is just a sensitive sensor on the fuel as the cheaper fuel doesn’t seem to affect the running of the car in any way.

    • Austin says:

      Very well could be. Thanks for sharing, I have heard of similar issues but have not experienced it with my personal cars nor hear from my customers about it here in Houston TX. Might try switching fuel providers and see if things change.

  16. Jake says:

    I recently purchased a 95 chevy s10. When I start the vehicle and drive nothing seems to be wrong, but as soon as I stop and let the engine idle, the check engine light comes on. Any idea of the cause?

    • Austin says:

      Humm strange. I would open the hood with the engine running and listen for a hissing noise that would indicate a vacuum leak somewhere. If the engine is having trouble maintaining idle speed or idle is too low I would look at the throttle body and have it cleaned as needed.

      Other than that we are going to have to have the computer codes read with a scanner and see what codes are stored and go from there.

  17. The yellow engine light only comes on for about 30 seconds and goes away. I have taken the car for a service at a Ford dealer and they say they have not found any problems. Any idea what could be wrong? Could it be a faulty sensor?

    • Austin says:

      The yellow light should come on along with the other engine lights whenever you start the engine then they should all slowly turn off once the onboard computer has check all compents and is happy things are ok. If it’s staying on much longer….there may or may not be a problem. I don’t think I would worry about it as long as it goes off and does not come back on when the engine is running. If it does you need to get the mechanic to check your computer “codes” while the light is on so leave the engine running so the light does not reset.

  18. Kim says:

    Hi there

    I have a 99 Corolla with check engine codes of P0125 P0130 and P0133.
    Is this a common combination with a possible simple fix like the loose gas cap you mentioned?
    I haven’t noticed any physical running issues or ‘changes’ in how the car performs.

    Thank you for this website!

    • Austin says:

      The 125 code means the coolant temperature was low when the computer checked it. Could be low on coolant or a faulty coolant tempurator sensor or nothing wrong at all and once the engine light is reset the code never returns.

      The other two codes are related to emissions gasses leaving the tailpipe and the fuel to air mixture not being correct. This could be a faulty oxygen sensor or an exhaust leak or some kind of vacuum leak under the hood.

      I would have the light reset and see what if any codes return and go from
      There. It’s not uncommon for all but one code return and the other codes were set because of the first trouble code issue. Make sense?

  19. sondra says:

    i have a 06 chevy equinox and the other day the red check engine light came on. now i did notice that after i got gas it came on can this be the problem?

    • Austin says:

      If the light is RED in color, it means you are low on oil, coolant, overheating, or the alternator is not charging the battery. In short, it’s something serious and the vehicle should not be driven. A YELLOW check engine light means there is an emissions sensor or some other sensor type of problem and should be looked at at your convenience. A loose gas cap can set a yellow check engine light sometimes.

  20. Francis says:

    i have a 2008 glant automatic and i was driving it like a stick. you know when you switch low into second and then third. after doing that for an afternoon drift, the service engine light came on. i recently took it in for an oil change. i really dont know why its doing this to mee. PLEASE

    • Austin says:

      I dont really know what that could have done to turn on the check engine light. I would drive the car normally a few days and see if the computer will reset itself and turn the light off.

  21. Casey says:

    I drive a 2001 Dodge Ram V8 Extended Cab Pick up truck and on Sunday October 24 I filled it up with gas. The morning of October 25 I noticed that the check engine light was on. Well I check the entire engine and nothing seems to be wrong. Is it just that the light won’t turn off or could it be the gas I put in it Sunday? Please reply back ASAP.

    • Austin says:

      Double check that the gas cap is on rightly and “clicks” when you turn it. A loose gas cap can cause a check engine light on…..and there are MANY other sensors that can also set the light, so if the cap is tight then you will need to visit your mechanic and get your computer codes scanned to see what has happened.

  22. kevin says:

    I have a 2003 stratus as i was driving home the car slowed down would not pick up when I hit the gas, and then all of a sudden it would go but then the engine light came on and is still on what could this be ?

  23. Judy says:

    The check engine light came on after I had put gas in about two weeks ago. I checked the gas cap and it was tight. I had the battery disconnected and reconnected and when I drove the car a short distance, it went off. It came back on the next time that I put gas in. I tried the battery disconnect again and it didn’t work. I put fuel injector cleaner in it a couple of days ago and put high octane gas in today. I did hear a click, click, click, buzz sound one time today. The car runs great. I can’t understand and I have read the car manual and looked lots on the internet.

    • Austin says:

      You are going to need to see a mechanic and have your onboard computer codes scanned to see what is or was happening to set the check engine light. It is most likely an emissions sensor that is out of whack, but with that click click click you mentioned it could be something more serious and should require immediate attention or you are likely to be on foot. 🙂

  24. Mark says:

    hi i’ve got a 06 ford focus and as i was driving the yellow check light came on for my engine and was just wondering what could cause that and before it came on about half hour before hand i rolled over a fox and would that have anything to do with it as it could have done something to one of the sensors

    • Austin says:

      ouch, poor fox! Yes, a sensor wire could have come loose or got damaged in the collision. I would have the underside of the vehicle inspected for loose wire and any other damage that could have been caused.

  25. Kal says:

    I just recently had my transmission fluid flushed and new fluid put in…..I drive a 2007 Tahoe 4×4.

    I noticed the check engine light came on…..Its the first time its ever come on. Could the flush have anything to do with it.

    • Austin says:

      I dont know what they could have done during the flush that would cause the check engine light to come on, BUT I have seen stranger things happen, so anything is possible. You might want to return to the shop and have them double check that a sensor was not unplugged or came loose during the flush. Sometimes the mechanics at fast lube places get a little too rough with the air cleaner box and can unplug a sensor there…..and I would bet they checked your air cleaner for a potential upsell. 🙂

  26. Maria says:

    I have a 2003 Ford Focus and it didn’t have the check engine light on when i bought it just like two weeks ago. What type of sensor can someone take out to make that yellow check engine light come on?

    • Austin says:

      I dont know what you mean by “take out” a sensor. Usually, USUALLY, a yellow check engine light comes on because of a problem with an emissions related sensor OR a running problem with the engine. If the engine missfires, like from a bad spark plug etc. etc. the light will come on because the computer saw a problem. You will need to visit your mechanic and have them read your onboard computer codes to figure out what is happening or what had happened to set the light. too many sensors to just guess.

  27. Davis says:

    Hello I have a 2003 Honda Accord 2.4 coupe. I recently just got a brake booster installed and now my check engine (yellow) light is on. Do you have any ideals what could of happen?

    • Austin says:

      Hummmm, maybe they left something unplugged during the install process?? This could be something simple like a sensor under the hood that was not plugged back in??

  28. travis says:

    My check engine light is on, so far nothing major has happened. The engine sort of shakes a little when moving slow though. Any ideas what this could be?

    • Austin says:

      Could be anything really, a faulty emissions sensor under the hood or a bad spark plug or spark plug wire causing an engine miss. A vacuum leak under the hood could also cause the light and the shaking so listen for a hissing noise under hood with the engine running. A mechanic and a computer scanner will probably have to look into this for you.

  29. kelly says:

    my dashboerd says check engine..can it also mean to replace the whole engine?

    • Austin says:

      If its a yellow light, its most likely a faulty emission sensor or and engine missfire or something along those lines. If you want a new engine, please come and visit my shop in the morning, I would be happy to install one 🙂 but you dont need it.

  30. Kyle says:

    I have a 94 Mazda mx6 and when I drive it for about 8 minutes or so the check engine light comes on. I was changing the oil the other day and I noticed I was leAking oil out of the oil pressure switch, could that be making the check engine light come on.

  31. Autumn says:

    I have a 2000 nissan altima. I have a major problem where all the instraments on the dash will go out an remain out for periods of time while i am driving. Gas, speedometer, temp, an rpm`s all go blank or they will freeze up. Also when i am driving more than 50 mph, the car will jus stop accelerating an start to slow down. I have to hurry up an shift it to neutral than back to drive, jus to get it to keep goin. I no longer beltway drive in my car because of this. It has been doin this since i purchased it used in may. Now recently the service engine soon yellow light, is on now. Is that related to my instrament panel or is that another thing wrong with it now? I am a single mother of 2 an i spent all my tax money on buyin the car, so now i am broke an cant pay for a diagnostic test to get done if it is only related to the instrament panel problem. Please help with some advice on what i should do now. Thank you 🙂

    • admin says:

      I would definitely have your check engine light looked into by the dealership if possible since this is not going to be a “normal” problem. The dealer would be the best place to have this sort of issue diagnosed, and you can decide if you want them to do the repair or to go elsewhere for a cheaper labor rate once you know what the problem is. I have not had personal experience with this issue but would read your computer codes and track down the engine light in hopes it would lead me to the dashboard issue. I would assume both lights and running problem are related to the lack of RPM signal.

  32. Jo says:

    I drive mazda 626 ’99 model. It wasn’t showing check engine light when I bought it newly but after 6months it started showing. A yr after I changed the engine sitting it went off only 2 appear that same day till now. Pls advice me what to do.

    • admin says:

      You are going to have to get a mechanic to read your onboard computer codes and see what is stored in your computer memory and go from there

  33. HEEELP! says:

    My Check Engine light came on today, but just for a moment. It was doing it b4, then my machanic fixed it. It was an emmisions problem. Now, I can tell you that I’m not good with changing the oil in my Honda Passport SUV 1995 & I know that’s NOT a good thing, but COULD THIS be the potential reason why the yellow “check engine” lgt DID COME ON? I don’t drive much AT ALL. Maybe 5,000 miles per year. Still, the oil should be changed & I’ve never changed it & have had it for over 2 years. Maybe 3.
    It’s also running rough. Hesitating too. I’ll have to give it some extra pumps on the gas pedal while driving. Could this mean NEED OIL CHANGE AS WELL?

    • admin says:

      No, lack of oil change is not the reason for the YELLOW check engine light….a RED check engine light can be a symptom of lack of oil or oil changing but not yellow. You most likely still have an emission sensor type of problem and need to see a mechanic and have them read your onboard computer codes to see what the problem is. FYI, a loose gas cap can also set a yellow check engine light so make sure your gas cap is tight.

  34. Tracy says:

    My engine light has been on for a while. I took it to a mechanic and he hooked it up to the diagnostic machine and it returned “#1 injector”. The car is running and has been running pretty good. It only has a slight hesitation when it first starts and once it gets going, I never have a problem. I am using the mid grade gas now thinking that it might be caused by trash or water in the gas. I have also put in a fuel injector cleaner. THe mechanic said it wouldn’t hurt to keep driving it. Please advise. Thank you.

    • admin says:

      I would try professionally cleaning the fuel injectors at your repair shop and see what happens. Continuing to drive like that probably wont hurt anything and might eventually clear up?

  35. Hamza says:

    My 1996 acura engine light is on for a while now, I have changed a lots of things and still on, could you help please?

    • admin says:

      You need to find a QUALIFIED mechanic and stop guessing at parts to replace. It could be many things, and I too would only be guessing from where I am.

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