Nearly everyone who has driven a car has likely seen their "check engine" light come on, but most people are dumbfounded by this occurrence. It can be especially frustrating the first time it happens, as it doesn't exactly indicate how serious the problem is. It's also a bit of a vague suggestion because it does not tell the driver what exactly they should be checking for.

In reality, the check engine light is vague on purpose. That's because the issue could be any number of things related to the engine. The check engine light does not necessarily mean you need to pull over and call for a tow truck right away. However, it's also not something that should be ignored for a lengthy period of time. Eventually, you're going to need to determine what precisely is wrong with your vehicle.

When the light comes on, don't panic. Many drivers' first instinct is that it's dangerous to continue operating the vehicle, but this isn't the case. The check engine light is the way things are supposed to happen in a vehicle - it means that the car has detected the issue and it needs to be taken care of. However, there are very few issues in a vehicle that would cause the car to suddenly become extremely dangerous.

A good rule of thumb is to think about what you're doing as soon as the light comes on. Did it happen as you sped up or slowed down? Had you been driving a long time or did the car just start up? Did you recently fill up the tank? This is all information that may be incidental, but it could also be useful for a technician to know about when diagnosing the vehicle.

Another thing to keep in mind is that your problem may not be a "hard fault." A "hard fault" usually indicates that something is broken or not working correctly. It's very possible that a "check engine" light will come on occasionally, or blink a few times and then turn off. This tends to indicate that something in your engine is not working at 100 percent efficiency, but it's not yet broken. These problems are likely extremely minor or intermittent and don't require your immediate attention. If the light stays on, however, it's probably a long-term problem.

However, other common causes of the "check engine" light coming on may be more serious. According to CarMD, the most frequent "check engine" problem is a broken oxygen sensor, accounting for nearly 10 percent of all issues. This is an important problem to fix because it will cost you money very quickly. An oxygen sensor is responsible for telling the engine the right mixture of air and fuel. Thus, fixing a broken one can improve your fuel efficiency dramatically. If you feel like you're running out of gas much more quickly than normal, it's a safe bet an oxygen sensor is to blame.

That said, there are many other issues that could trigger the light. Spark plugs and wires, catalytic converters and mass air flow sensors are all issues that will need replacement, although a driver may be able to handle the repairs on their own. A mechanic, however, can use the car's diagnostic system to read any error codes and then let the driver know what's wrong. Many places provide this service free of charge.

Before you head to the garage, however, check your fuel cap! As it turns out, not screwing this cap on all the way is second only to the aforementioned oxygen sensor as the cause of a check engine light.