The check engine light, although mostly a sign that something is seriously wrong with your car, can also come on for seemingly simple or trivial reasons. For example, a loose gas cap is enough to trigger the check engine light. Regardless, a check engine light shouldn't be ignored. The severity does depend on the state of the check engine light, though. If it's lighting up and remains constant, then it might not always indicate something serious. However, if the check engine light is flashing/blinking, then you need to have it diagnosed and fixed right away. A blinking/flashing check engine light is an indicator that a major component of your car is failing or has already failed. Thus, you should avoid driving your car, and call in a mechanic to diagnose what's wrong.