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Updated on June 11, 2011


Have you ever been driving down the road and all of a sudden your check engine light comes on out of the blue? If so, that light is on for a reason. If you already have a check engine light on, and your not sure why it is on, you have came to the right place.

If you have a check engine light on, it is on because your computer has detected a problem with your vehicle. The computer in your car is set up to alarm you when it senses that something is wrong with the vehicle. There are a number of things that can trigger your computer on your vehicle. When it comes on, you may notice a difference in your vehicle's performance. Sometimes, there will be no change at all. None the less, if your check engine light is on, you need to have it checked out.

To be honest with you, there are over a hundred different things that can cause your check engine light to come on. Some things may be simple while others are more complex and difficult to deal with. So how do you find out what is causing it? You have a small hookup under your dash panel. This is where the error code tester hooks up to troubleshoot your computer and check engine light. If you are like many of us, we don't even own this gadget. If so, that is fine. Anytime you have a check engine light on, you can take your vehicle to Autozone, Napa, or Advanced Auto to have their staff scan it for you. And the best part of it all, it does not cost a dime. It is totally free. They will hook up the computer for free and they will be able to tell you exactly why it is on and they will be able to guide you to the parts you will need to fix your problem.

You can't beat the price and quality of this OBD scanner.
You can't beat the price and quality of this OBD scanner.


      It is necessary to perform the computer reading on your vehicle to find the exact problem with your vehicle. Many vehicles have over a hundred different codes for specific parts on your car or truck. When you hook up the OBD tester to the car, the computer reader will put out a list of error codes. Once you have the code, you need to refer to your Haynes manual to diagnose the meaning of the code. If you take it to an auto part store, they will do this for you and it still doesn't cost anything. Once you know the meaning of the code, you will know exactly what part you need to fix your vehicle.

     Many of the cars on the road today have the OBD II system. This system includes your Powertrain Control Module (PCM). The computer works with all your information sensors to keep an eye on the performance of your vehicle. Once it notices a change of any kind, it will pick up on it and send the information to your PCM. The PCM stores this data and your check engine light will come on. You can use the OBD II scanner to find the stored codes in the PCM. Your information sensors are your oxygen sensors, crankshaft sensor, camshaft sensor, intake air temperature sensor, mass airflow sensor, vehicle speed sensor, engine coolant temperature sensor, throttle position sensor, manifold pressure sensor, and transaxle sensor. Each vehicle has different sensors and they may not be the same that is listed. All these sensors send information to the PCM when the sensor picks up on something that is wrong. They send it to the PCM, it is stored, and your check engine light will appear on the dash panel.

     The PCM is the brain of your vehicle. The PCM controls all the fuel and emission systems electronically. It receives input back from the information sensors and it generates signals to relays and solenoids on your vehicle. Your vehicle needs air, fuel, and fire to start and run. The PCM controls all of that. If your system is off by just a fraction, your vehicle will not run right. Your PCM is in charge of the spark plugs, coils, wires, coil packs, distributor, and many other things. 


      In most cases, when your check engine light is on, it is on constantly. In some cases, your light may be flashing. There is a reason for this and it is not good news. If your check engine light is flashing, this may mean that you have major engine damage. If this is your case, be sure to drive your vehicle to a part store and have it scanned as quick as possible. The same can be said for those who have the light on constantly. The check engine light in your vehicle is on because there is a problem. Get it check out soon. Many times before, when a problem isn't fixed quick, the problem becomes worse. There are parts in your vehicle, when bad, can cause other parts to fail. And in the end, you have one big mess that could have been avoided.

     Remember, there are many thing on the vehicle that can cause your check engine light to come on. Before you can find the exact cause, it must be read by an OBD II scanner. If your light is on, get it checked out as soon as you can. The quicker you solve your issue, the better off you will be. It may be just a simple problem, but it may be one of those parts that can cause the others to fail if it is not fixed. It is not worth taking the chance.


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    • profile image

      anonymous 4 years ago

      Disconnect the cables from the battery terminal for 3-5 minutes clears off the check engine lights, or reset the computer box

    • Richard83 profile image

      Richard83 6 years ago from West Virginia

      Eventsyoudesign, thank you so much for the comment. A bad power connection can cuse the light to come on. I appreciate your thoughts and thanks. I will see you soon.

    • eventsyoudesign profile image

      eventsyoudesign 6 years ago from Nashville, Tennessee

      I need to have my husband read this article. He will be interested in this information. His check engine light was on a while back. All he did was clean the cables on the battery and replace the battery and the light went off. I don't know what made him think of the battery but it worked. I know in Tennessee if the check engine light is on and you don't fix it you cannot pass an emissions test at MARTA because they won't even look at your car. Thanks for a great article. Teresa

    • Richard83 profile image

      Richard83 6 years ago from West Virginia

      Thank you so much Denise. It is always good to know or have a mechanic around for things like this.

    • Denise Handlon profile image

      Denise Handlon 6 years ago from North Carolina

      Very good advice. It always serves as an alarm for me when I see this flashing. Fortunately, I have a good friend who is a mechanic. Thanks for sharing this useful info.