Imagine driving home from the office and suddenly noticing the "check engine" light is displayed on your dash. What should you do? Many of us have heard this light is one of the worst possible lights to see because it suggests expensive repairs. Moreover, most drivers have no idea what they should do in the event they see it.

Below, we'll provide an overview regarding your check engine (CI) light. We'll describe how it works, the most common reasons it turns on, and how you should react when you notice it. We'll also give you a few tips for troubleshooting the culprit that triggered it.

How The Light Works

The CI light is actually part of an older automotive design. It is connected to your car's onboard diagnostic system. This system is built around a computer that monitors and regulates several features of your vehicle's operation. For example, the computer watches your engine's RPMs, the air-fuel mixture within the individual cylinders, and its ignition timing. It may also control the shifting of your transmission, depending on your vehicle's make and model.

When a problem occurs, the on board diagnostic system will attempt to correct it. If it is unable to do so, it will trigger the check engine light. Whenever the computer sets off the light, it will generate a trouble code. This code helps the mechanic determine what is causing the problem. For example, a failing oxygen sensor will produce a different code than a misfire.

Your mechanic will have access to a special diagnostic tool that can "pull" the code from the computer. You can also purchase a similar tool at many auto supply stores. Automakers create the trouble codes to make it easier for technicians to find and resolve problems.

It's worth noting that every automaker designs their onboard diagnostic system a little differently. That means the computer in one type of vehicle may set off codes for different events than another vehicle's computer. That said, there is a significant amount of overlap. For example, nearly all automakers have designed their computers to identify most types of powertrain issues.

Knowing How To React

So, what should you do if you notice the CI light illuminated on your dash? The worst thing you can do is ignore it. A lot of drivers see the light and convince themselves they have plenty of time to have the issue addressed. The problem is, there's no way of knowing whether something serious is wrong with your engine or another major component. A lot of issues start small and worsen with time. When your engine is involved, this can lead to extensive - and expensive - repairs.

To be clear, there's rarely a need to pull over immediately when you see the CI light. However, if it comes on, avoid letting too much time pass before having a mechanic pull the trouble code. Drive to a repair shop and ask a technician to pull the code as soon as possible. Then, once you have determined if the issue is serious, you can decide whether you can postpone the necessary repairs.

A Few "Common Sense" Tips

When you see the check engine light come on, try to identify other signs that imply a potentially serious problem. For example, a low oil level should trigger a dedicated light, but may also set off the CI light. Because insufficient oil can cause your engine to overheat, you should pull over until you have a chance to replenish it.

Also, the light can often be triggered by a loose gas cap. If you have recently refueled your car, check the cap to make certain it is tight.

If you're driving a GM vehicle and subscribe to the OnStar service, call a representative as soon as you notice the CI light. The representative can remotely pull the trouble code and determine the problem.

The purpose of your car's check engine light is to notify you of any issues that need to be resolved. If you notice it illuminated on your dash, have the underlying issue identified and fixed as soon as possible.