The Check Engine light, which is officially called the "Malfunction Indicator Lamp" (MIL) alerts you when your vehicle's OBD II system has detected a potential emissions problem. Depending on the nature of the problem, the Check Engine lamp may come on and go off, remain on continuously or flash. Of course, none of this gives you any clue whatsoever as to what might be going on.
Some people panic when they see the light, fearing their engine is experiencing some kind of major problem. But fear not, because in most instances, the problem is usually minor and is nothing that requires your immediate attention
Here's how the Check Engine Light works. When the OBD II system detects any fault that may cause an increase in emissions, it sets a "pending code" in the computer's memory. The Check Engine Light doesn't come on yet because the system needs to make sure the problem is real and not a temporary glitch. If the same problem occurs on a second trip (under the same driving conditions), the OBD II system will then set a diagnostic trouble code (DTC) and turn on the Check Engine Light.
WHAT TO DO IF YOUR CHECK ENGINE LIGHT IS ON
If no other warning lights are on (temp, oil pressure, charging, etc.), AND your vehicle is driving normally (no unusual sounds, smells, vibrations, loss of power or other signs of trouble), you don't have to do anything immediately. But you need to find out why the light came on when it is convenient to do so.
USE A SCANNER TOOL
the only way to know why your Check Engine light is on is to connect a scan tool or code reader to the 16-pin OBD II diagnostic connector under the instrument panel and read out the code. If you do not have a code reader or scan tool to do this yourself, you can take your car to an auto parts store for diagnosis.
