First I'll give you a little background on what turns on the check engine light. Basically the federal government wants to notify the driver that the vehicle may be contaminating the atmosphere. Yes, the main function of this light is for emission system compliance.

The check engine light comes on to notify the driver that a code has been set in memory. Sometimes the code relates to a serious problem, but in most cases it's a minor malfunction or intermittent condition.

If you have your own auto scan tool. You can answer the number one question in everyone's mind when that service engine soon light comes on. Of course the question is, why is this light on. An auto scan tool can give you the answer quickly and easily.
The automotive scan tool is a lot easier to read and use than most people realize. Your auto repair center is counting on you not finding this out.
Automotive scan tool or car code reader. This is my second article on the subject of why everyone should have one.

Connecting the auto scan tool to your vehicle and pulling out the codes and then resetting the light is your auto repair shops favorite job. They don't have to get dirty or bust their knuckles, and it pays very well.

In this next example of using an automotive scan tool and reading scan tool data. I'm going to give you a very common code that you could find set in the computers memory. I come across the oxygen sensor voltage low or high code all the time. Many mechanics when they find this code just want to go ahead and replace the oxygen sensors. This may not be the right thing to do.

When you pull this code up on your automotive scan tool, the first thing you want to do is reset the code and see if it returns. If the check engine light has come back on and this code has reset the second thing you want to do is read the data stream for the oxygen sensors. Reading scan tool data for this code using the automotive scan tool is a lot easier than you would think.

Mark is a certified master mechanic that has set up a car questions website for the do it yourself auto mechanic. You can see the scan tools he uses at his auto scan tools reviews page
You can also learn more about check engine lights and reading scan tool data from several free articles at the bottom of this why you should own an automotive scan tool page.