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Ignoring your check engine light could have expensive c... Ignoring your check engine light could have expensive consequences (p_x_g, Flickr).
It glows on your car's dashboard and instantly ignites terror and loathing in the hearts and wallets of drivers; the dreaded "Check Engine" warning light.

For some, it is a minor irritant to be ignored. Even Public Television's "Car Guys" joke that the remedy is to put a piece of duct-tape over it. Some cynics believe the "Check Engine" light was invented to get vehicle owners to schedule more visits to the dealer for service. Some cars, after all, seem to have such a sensitive "Check Engine" light, and driving over a stick of gum is enough to flick it on.

Before making any assumptions about what to do, though, or whether a call to the dealer's service department should be an automatic response, it is a good idea to understand the light and what makes it come on.

What is it?

The check engine light is usually a warning lamp on the instrument panel of your car that lights up when the car's engine computer detects a problem. All cars have some sort of on-board diagnostic system, though some higher-end models may supplement the simple light
with a more detailed graphic display to provide additional information about what's wrong.

How does it work?

When the check engine light flashes briefly, it means the car has experienced a momentary problem. These hiccups happen sometimes, but aren't much cause for alarm. If the check engine light comes on and stays on, however, that's an indication of a problem that could be
serious. If the check engine light blinks constantly, you need to stop your car immediately, as it has experienced a major malfunction and continuing to drive the car could cause serious and wallet-wilting damage to the engine or even lead to a dangerous situation.

But the check engine light in modern cars is more than just an "idiot light" as it was once called. Since 1996, all cars sold in the United States have been required to have something called OBD-II in them. "OBD" stands for On-Board Diagnostics, and it's a standardized way for the engine control computers to report problems. When the check engine light comes on, the system records a code that corresponds to the problem the engine computer experienced. If you look under your dashboard on the driver's side, there's a funny little connector that looks like it belongs to a video game system. That's the OBD-II port, and if you plug in the proper equipment, the computer in the car can tell you what went wrong.

The neat thing about OBD-II is that it's ubiquitous. While some manufacturers have equipped their cars with other proprietary diagnostic ports for their specific dealership service technicians, OBD-II is the same on every car. This means that it's easy and cheap for mechanics and do-it-yourselfers to buy what's called a "scan tool" or use a laptop and some specialized software to connect to the car and download the fault code from the OBD-II system. CarMD is one such service that consumers can buy into and use to diagnose their own vehicles.

Why would I want it?

You certainly don't want your check engine light to come on. But if it does, downloading the fault code from the OBD-II port to one of the after-market program on your computer, such as CarMD, can tell you what the computer thinks went wrong with your car. Sometimes these errors are just simple things: Often the check engine light will illuminate when the gas cap has not been tightened. But other times, serious errors will be reported, like problems with the catalytic converter or conditions that cause the car to run rough or lose power. While these problems will all make your check engine light glow like a Christmas tree, the big advantage to OBD-II is that once you know what the computer in your car thinks went wrong, it can make it much easier to diagnose and repair the problem. That means your mechanic takes less time to make the repair, and you spend less paying the mechanic.

Is there any downside?

There is one big criticism of the check engine light system, which is that when it comes on, it doesn't really tell the driver enough. Since the range of problems that can cause the light to activate is so broad, drivers don't know what to do when they see the light.

Is it a small problem, like the gas cap not being tightened? If that's the case, than a trip to dealer or mechanic can be a huge waste of time and money. But if the issue is more serious and gets ignored, there is a risk of damage to the car. If a dealer sees that the check
engine light was on, but the owner kept driving the car, that can become grounds to void the warranty on the damaged parts. If ther car is still under warranty, the best idea is to just take it to the dealer. Anything wrong should be covered.

What vehicles offer it?

Every vehicle sold new today has an OBD-II port and some sort of illuminated check-engine light.

Bottom line

Understanding what t means when your check engine light comes on, and how to best respond to it can help you keep your car running well, creating less pollution and saving you money.



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    • 1 Second Ago
  • 477 Comments
      Phil Collins
      • 3 Years Ago
      Please do something when your Engine Light comes on I didn't and my wife left me,the dog ran away and now my favorite Country and Western Station won't come on. Rocketman <> St. Louie, Mo.
        Lita
        • 3 Years Ago
        @Phil Collins
        Your wife left and your dog ran away for other, more obvious reasons.
      • 3 Years Ago
      My problem is The "ABS" light is on most of the time with the brake light. Mechanic sais no Problem. DUH
      • 3 Years Ago
      My check engine light stays on when the gas cap has not been screwed in tightly. Once you tighten it, after two or three engine restarts, the light goes out. This is a Toyota RAV4.
        iagreg
        • 3 Years Ago
        I took my car in for a state inspection and they said the gas cap was bad. Paid $15 for a new one. A few days later the check engine light came on and Autozone ran a scan which said there was a problem with the evaporative contol system, which includes the gas cap. I took the new cap off, put the old one back on and the check engine light went off. Most mechanics nowadays couldn't find their butt with both hands. I trust myself to do the work more than some $75/hour high school dropout.
          you knucklehead
          • 3 Years Ago
          @iagreg
          Where the heck do YOU go?? I have 6 guys working for me, and they all have at least 2 years of college. Stop shopping price and start talking to other folks that own the same type of cars as you. People are always ready to relay their bad experiences, but will only talk about the good ones if asked.
          ExAstrisScientia
          • 3 Years Ago
          @iagreg
          @iagreg, I had a problem with the dash lights caming on but, there wasn't enough juice going to the engine to start it. My mechanic found that a battery cable had slipped down and was barely making contact.. He reconnected it, did a few more test to make sure that was the problem and only charged me $50. He could have ripped me off and said the problem was the alternator or the electrical system. So, don't go saingy that MOST mechanics are incompetent or dishonest.
      wdodf
      • 3 Years Ago
      If your check engine light comes on, go to the nearest Auto Zone or O'Rielly's Auto Parts Store. They will connect a scanner to read the trouble code and will print you a slip telling what is wrong. Then you can go to your mechanic and get the problem corrected or just fix it yourself. Many trouble codes will tell you that some sensor needs replacing. Most are eaisly accessable.
      zhappygiver
      • 3 Years Ago
      Black tape helps
        johnjhenry1
        • 3 Years Ago
        @zhappygiver
        not really, you didn't fix anything. ignoring a problem does not make it go away
      george
      • 3 Years Ago
      Kia1001 has the answer. I recently had a check engine light come on. Went directly to Advance Auto and the counter girl plugged a hand-held analyzer in my data port (car's data port that is) and the diagnostic was that the oxygen sensor was bad. It was a screw out/in part much like a spark plug. Bought one and changed it out. Had to go back to Advance and have the lady use her analyzer to clear the alarm. Started getting much better gas milage immediately. The service is free but of course the part isn't.
        grimesclrcbg
        • 3 Years Ago
        @george
        I to one time regarding the above Corvette I own and spoke about above . The CEL came on, they scanned my car and all I needed was a new gas cap. I bought the new gas cap and put it on myself, problem was solved.
      • 3 Years Ago
      If the check engine light flashes that means the transmission have problems be careful.
        Mark Lathom
        • 3 Years Ago
        Your "Engine" and "Tansmission"are two separate parts.
          johnjhenry1
          • 3 Years Ago
          @Mark Lathom
          two seperate parts that bolt directly together. yes the check engine light will come on if there is a problem with the transmission
        wrxfrk16
        • 3 Years Ago
        That is just one of the thousands of things that could trigger a check engine light. If it is a serious trans problem, you should be able to feel it when shifting or there should be symptoms present that you can pick up on if you drive the car on a regular basis.
        johnjhenry1
        • 3 Years Ago
        it can also mean a problem with the engine
          snoridernlv
          • 3 Years Ago
          @johnjhenry1
          a flashing check engine light usually signifies the engine is currently experiencing an active misfire. In other words, one or more of the cylinders is not burning the fuel properly. That can be costly because the unburnt fuel due to the misfire passes through the catalytic convertor, causing the convertor to heat up and become restricted over time. A catalytic convertor could run hundreds of dollars to replace. By the way, transmission control modules on all modern cars will also set the check engine light when they experience a sensor fault. So that light can be tied in with your transmission also.
      • 3 Years Ago
      Incase you didnt notice , at the start of this artical it keeps saying about buying a scanner . that is what this is all about . most people are not gonig to be able to fix the problem . being a tech myself i know unless the engine is running bad or the trans is acting up on you the car will run fine . an so you all know when the check engine light is on it also means the computer is controling everything . So unless it is something very serious its not gonig to shut your car down . its all a big fat scam .
      Nancy
      • 3 Years Ago
      They are still DUMMY lights if they don't tell you WHAT the problem is...how about some basic information...lol.
      accsport
      • 3 Years Ago
      This thing is called the "Maintenance Indicator Lamp" or MIL which the idiot that wrote this story should have known and been much more specific about this thing. To all of you who are not sure of this indicator find someone to read the OBDII Code for it immediately whether it is Autozone, a friend like me who has a scanner, or someone but do not wait. It could a low temp error sometimes pulled on cold days when you are driving before the engine, and its not a motor as motors are electric, has not warmed up or a major problem such as a crank sensor which will lead to expensive engine failure. Your choice.
      Unicorn1440
      • 3 Years Ago
      My check lights has be coming on even after I fix the problem , so I now do not even believe it works right any more,
        chzyrider
        • 3 Years Ago
        @Unicorn1440
        Perhaps there is another code to address. Or you did not fix the real problem or actual cause of the trouble code. Learn what the code number is that is triggering the light and always TEST the related components first, most electronic sensors can be tested for proper function with a simple multi-meter. Don't just start replacing parts in hopes of curing the code. If a shop did the work for you, take it back, but be nice. It's easy to miss a random or an intermittent cause of the trouble code if it does not trigger while the mechanic is testing it.
      Ronald Smith
      • 3 Years Ago
      Screw the Check engine light , It stays on in my car 24/7 and it runs great , I take out the fuse and reset it when I get my tag once a year to pass the test , also its someting that I have already put a peice of black tape on .I have a 1999 Mazda 626 that has 215,000 miles on it and keeps going , ugly car but rides and runs great . I say cut the freaking cord on the Check Engine Light , any moron knows not to drive a car hot or out of oil , all else is a waste of money and time. People get wise to this crap !! Hello . Set up your mechanic and see if he is telling you the truth about the problem , also changing the oil ever 4,000 miles is a joke to and a rip off get real ...
        hgeorgech
        • 2 Years Ago
        @Ronald Smith
        Ronald .. hey, changing the oil every 4 - 5,000 miles seems reasonable (many newer cars since '08 recommend 5 - 7,500 miles with semi-synthetic oil) - ya know, kinda like taking a bath on Saturday night whether you're dirty or not ... oil .. and soap are reasonably cheap!
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