How long have you been enjoying the romantic glow of your check engine light? Hey, it’s not there to create ambiance – it’s a warning that something’s wrong.

When your check engine light comes on; get it checked. Many conditions that cause the check engine light to come on affect fuel economy. Some very dramatically.

Always make sure you tighten your gas cap until it clicks. A loose gas cap can cause a false sensor reading that’ll make the check engine light come on.

If your date’s eyes are smoldering in the reflected glow of the check engine light, try to think of all the gas money you’ll save by getting it fixed.

Have you ever had an experience like this? You drive through the one of those automatic car washes. When you get to the end, where the dryer is blowing, your check engine light started flashing!

You fear the worst, but within a block or two, the light stopped flashing, but stayed on. By the next day, the light was off.

You wonder; “What was going on?” Well, it’s actually a good lesson in how the Check Engine light works.

Your air intake system has a sensor that measures how much air is coming through it. When you went under the high-speed dryer, all that air was blasting past the sensor. Your engine computer was saying, there shouldn’t be that much air when the engine is just idling. Something’s wrong. Whatever’s wrong could cause some serious engine damage.

Warning, warning! It flashes the check engine light, to alert you to take immediate action.

It stopped flashing because once you were out from under the dryer, the airflow returned to normal. Now the engine control computer says the danger is past, but I’m still concerned, I’ll keep this light on for now.

Then the Check Engine Light goes off in a day or two.

The condition never did recur, so the computer says whatever it was, it’s gone now. The danger is past, I’ll turn that light off.

Now a flashing check engine light is serious. You need to get it into the shop as soon as possible. But if it stops flashing, so you have time to see if the problem will clear itself or if you need to get it checked. How does the computer know when to clear itself?

Think of it this way. The engine control computer is the brain that can make adjustments to manage the engine. Things like alter the air to fuel mix, spark advance, and so on. The computer relies on a series of sensors to get the information it needs to make decisions on what to do.

The computer knows what readings are in a normal range for various conditions. Get out of range, and it logs a trouble code and lights up the check engine warning.

The computer will then try to make adjustments if it can. If the computer can’t compensate for the problem, the check engine light stays on.

The computer logs a trouble code. Some people think the code will tell the technician exactly what’s wrong?

Actually, the code will tell the technician what sensor reading is out of parameters. It can’t really tell you why, because there could be any number of causes.

Let’s say you’re feeling hot. You get your heat sensor out – a thermometer – put it under our tongue and in a minute or two you learn that you have a fever of 104 degrees.

You know your symptom – a fever – but you don’t know what’s causing it. Is it the flu, a sinus infection or appendicitis?

You need more information than just that one sensor reading. But it does give you a place to start and narrows down the possible problems.

There are reports on the internet telling you that you can just go down to an auto parts store and get them to read your trouble code or buy a cheap scan tool to do it yourself.

There are two problems with that. First, the computer stores some trouble codes in short term memory, and some in permanent memory. Each manufacturer’s computer stores generic trouble codes, but they also store codes that are specific to their brand.

A cheap, generic scan tool, like you can buy or that the auto parts store uses, doesn’t have the ability to retrieve long-term storage or manufacturer specific codes. Your service center has spent a lot of money on high-end scan tools and software to do a deep retrieval of information from your engine control computer.

The second problem is that once you’ve got the information, do you know what to do with it? For example, a very common trouble code comes up when the reading on the oxygen sensor is out of whack.

So the common solution is for the auto parts store to sell you a new oxygen sensor, which are not cheap, and send you off on your way. Now your oxygen sensor may indeed have been bad and needed replacing. But the error code could have come from any of a dozen of other problems.

How do you know the right solution? Back to the fever analogy, do you need surgery or an aspirin? Leave it to the pros.

Today we’re going to talk about on-board diagnostics and the questions we hear from viewers who need answers about diagnostic services. They want to know what diagnostics are, what’s involved and what the benefits are. They really want to understand the value of diagnostic scans by a trained technician.

These are valid concerns. If you don’t understand something it’s really hard to know its value. Let’s start with some history.

Since 1996, all cars and light trucks have been required to use a standardized diagnostic system to help repair technicians determine what’s wrong with your vehicle. The diagnostic system works with the vehicle’s Engine Control Module – the computer that controls many engine functions.

The computer monitors dozens of components and processes. Depending on what the sensors read, the computer will make adjustments to compensate for conditions and minor problems. When there is a condition that it can’t adjust for, the computer will turn on the check engine light.

It is also called the “service engine soon” light on some vehicles. The warning light signals you to get into a service center so that the trouble code can be read and the problem can be fixed. Your service center will have a scan tool and powerful software that will help the technician diagnose the problem.

If you’ve searched for check engine light on the internet, you may have seen that you can buy an inexpensive scanner or go to an auto parts store to have the trouble code read to tell you exactly what’s wrong.

That’s a common myth. The code itself doesn’t tell you what’s broken. It starts you looking in the right place. It tells you what engine parameter is out of range – but it won’t tell you what’s wrong or how to fix it.

Let’s say you think your daughter has a fever. You take her temperature and it reads one 102 degrees. You’ve confirmed a fever, but you don’t know what’s causing it. Is it a 24 hour flu, an infection, appendicitis or leukemia? A fever is a symptom of all of these medical problems, but it takes a skilled physician’s examination and additional diagnostic tests to find out what is actually causing the fever.

An example of a trouble code could be: P0133, which reads “Bank 1 sensor 1 circuit slow response”. This means that the front oxygen sensor has a slow response time to changes in the air-fuel mix. If that’s all you knew about cars, you would think your oxygen sensor was broken and would replace it. Now, it could be the oxygen sensor – but it could also be a bad or contaminated airflow sensor, exhaust leak, electrical problem, an intake manifold leak or any of a number of other things.

You can imagine a lot of oxygen sensors have been replaced because of that code. So the on-board diagnostics point the way to where the trouble lies, but it takes some skill and high-tech equipment to actually pinpoint the problem. The cheap scan tools that a consumer can buy do not have the ability to retrieve some of the operating history that’s stored in the engine control computer. That history’s very helpful in diagnosing the problem. Service centers invest a lot of money in high-end diagnostic tools to help solve the mystery and get you back on the road as soon as possible without replacing a lot of parts that don’t need replacing.

So, on-board diagnostics provide a powerful starting place for a highly-trained, well-equipped technician to get to the bottom of your problem. When your check engine light comes on, get it checked. If the light burns steady – don’t panic. Get in soon to have the engine scanned. A flashing check engine light means that there is a severe engine problem. Get in as soon as you can – waiting too long can lead to very expensive damage. And try to not drive at high speed or tow or haul heavy loads with a flashing check engine light.

See more automotive videos on our Auto Video Tips library.

Did you know that today’s cars carry more computer power than the Apollo 121 Lunar Module that landed on the moon in 1969? New cars have as many as 12 networked computers and over five miles (eight kilometers) of wiring.  In fact, for the last decade or so, computers have been controlling about 85% of your vehicle’s functions.

Cars have sensors for manifold air temperature, coolant temperature, manifold air pressure, airflow, throttle position, vehicle speed and oxygen content. All of this electronic wizardry is pretty complicated.  So how do you know when there is a problem?

It’s simple – the Check Engine light comes on.  The computer monitors all the sensors and uses that information to decide what to adjust such as the fuel mix, spark timing and idle speed. In addition, the computer monitors its own circuits.  When it finds a fault, it turns on the Check Engine light and stores a trouble code in the computer.

It can be pretty disturbing when the Check Engine light comes on.  We wonder just how urgent it is. Generally speaking, it is not critical like a temperature or oil pressure light.  When you get one of those it means STOP NOW!  When the Check Engine light shows up, you should get to your service center to find out what the matter is as soon as possible.

Since 1996, there has been a strong emissions control component to the Check Engine diagnostic. But if your Check Engine light flashes on and off, you know that it is more urgent and you need to get it checked immediately to prevent damage.  You should slow down and avoid towing or heavy loads until you can get it checked out.

Your technician has special diagnostic equipment that will retrieve the trouble code from the computer and help him determine what is wrong.  From there, he can fix it and get you back on the road.