If you are referring to The Check Engine Light, then it comes on when the ECU (computer) detects a problem with the emissions system. It can be as simple as a loose gas cap or many other more serious things. Take the car to your local Auto Parts Store where most of them will scan the ECU for free. They will retrieve the code or codes that have been set. These codes will tell you where to start looking for the problem. It will not tell you the part that is defective only the part that is being effected. It takes knowledge and diagnostic skills to determine exactly what is wrong. Unless you are skilled at diagnostics then you should take the car to a professional for repair instead of just throwing new parts at the problem hoping one of them fixes it. You could spend lots of money and still not fix the problem,
If you don't feel anything different, it's an O2 sensor that is starting to fail.
The "check engine" light is misleading... It should be "something is wrong with your smog system and you need to pay us money to make the light stay off"
Funny ronich69. Engine light is kicked off from sensors, there are many! If they detect or as Ryde, On said fail, which is common, it will trigger a light. Usually you can go to one of the Auto Parts stores and they can read the light and tell you what if anything you need to do. Many times it is replace the sensor and see if it come on again, I will just clear the light and see if it come on again.
Without the code and make and model this is all I can say. Good luck.
It means one of the many sensors has detected a problem ,,,,,,, that or a sensor it's self has failed .
