A check engine light (also called trouble indicator or malfunction indicator) will come on when something in your vehicle isn't right, but it doesn't always tell you what the problem is. The check engine light will come on for a wide variety of reasons - some are issues that can be safely ignored while other issues require your immediate attention.
Types Of Check Engine Lights
Most cars are equipped with several different check engine lights. The most common lights include:
- Check Engine
- Brake (emergency or parking)
- Service Engine Soon
Examples Of Check Engine Lights
Below are a few of the many different indicator lights that you might have in your car. 
There are times when an indicator light is falsely triggered by too much methanol, ethanol, or other fuel additives.  Having your car checked will let you know if the triggered
What To Do When An Indicator Light Comes On
Some lights are obvious as to what the source of the problem is (i.e. battery and oil), if not the specific cause, but the more generic lights (check engine) are not. The best thing to do if one of your engine lights comes on is to use an automatic code reader (ACR) to determine the cause of the light.
Any vehicle repair shop or dealership will have an ACR and there is usually no cost to have them use an ACR on your car. Or, you can take your car to a car store, such as Auto Zone, where they will have ACRs that they can use on your car. Best of all, this service is free and you might be able to buy the parts you need to fix the problem yourself, all in one stop. Another option is to buy an ACR for your own use, but there really isn't a need to do this with so many free options available.
After you find out the reason for your check engine light, you can decide what to do. Most causes should be fixed within a reasonable period of time, and some should be fixed asap.