Check Engine Light is On
The Check Engine Light (which is actually the Malfunction Indicator Lamp or MIL) alerts you when an emissions-related problem occurs with the engine control system or emission controls on your vehicle. Depending on the nature of the problem, the Check Engine Light may come on and remain on continuously or flash. Some intermittent problems will make the Check Engine Light come on only while the fault is occurring (such as engine misfire). The Check Engine light usually remains on once a fault has been detected, and will remain on to remind you that a problem has occurred that needs to be investigated.
An illuminated Check Engine Light can be annoying because you don't know what's wrong, and whether or not the problem might be a serious one or just a minor fault. There is no way to know what the problem is until you plug a scan tool into the vehicle's diagnostic connector and read out the code(s) that turned the light on.
If no other warning lights are on, and the engine seems to be running normally (no unusual noises, smells, vibrations, etc.), you can assume the fault that is causing the Check Engine Light to come on is probably minor and won't hinder your ability to continue driving. But if other warning lights are on, you should probably stop and investigate the problem.
When the Check Engine Light comes on, a diagnostic trouble code (DTC) is recorded in the powertrain control module (PCM) memory that corresponds to the fault. Some problems can generate more than one trouble code, and some vehicles may have multiple problems that set multiple trouble codes.
The check engine or mil light is triggered by the power train control module (compute) that operates the engine and of late the transmission also. This happens when the monitoring system in the PCM detects a fault or noncompliance with parts and/of systems that control or effect emissions. Sadly there is only one light and hundred of issues that will turn it on. The operating system;s complexity makes it difficult for most care owners to understand, suffice it to say, have the system scanned to find out what is wrong. Ignoring the light not only means it is out of compliance emission wise, but the engine or some of the emission components may be damaged by continual use.