Reading scan tool dataReading scan tool data for most do-it-yourself mechanics is a simple matter of retrieving the code and identifying what the code means.
You will also probably be clearing the code and testing the vehicle to see if the check engine light code returns. If you own a more advanced obd 2 automotive scan tool. You will be able to pull up the data stream and read the scan tool data in real time. See my page about inexpensive scanners that can read the data stream at Automotive scan tool reviews obd 2 scan tool example
Lets say your vehicle sets a code for the coolant temperature sensor. You can then read the scan tool data for the coolant temperature circuit. You will be able to monitor the coolant temperature in Fahrenheit or Celsius and the sensor voltage in real time. If the vehicle is cold, you can then start the vehicle and watch the coolant temperature, voltage rise on the obd 2 scan tool. This verifies the correct operation of the sensor. If the coolant temperature and voltage remains a fixed value, yet the vehicle continues to warm up, you may have a dead coolant temperature sensor or bad wiring between the sensor and the computer.
Just because the computer sets a code for a specific sensor does not automatically indicate that that sensor has failed. More often than not, the sensor is working correctly and making you aware of a problem with the vehicle. For the above example of the coolant temperature sensor, if we have set a coolant temperature sensor code and when reading scan tool data the voltage increases as the vehicle warms up. The sensor is working correctly. In this scenario, the code may have been set due to a stuck thermostat, causing an overheating condition. Or even a stuck open thermostat, not allowing the vehicle to reach its proper operating temperature. Reading the scan tool dataThis gives you a clear path of diagnosis. The best way to approach the repair of the vehicle that has set a diagnostic code is to use the diagnostic tool, in combination with a quality online auto repair manual.The online auto repair manual will provide step-by-step diagnostic troubleshooting procedures with component location diagrams for that particular failure code. Using these tools together can save you a lot of time and money in replacing unneeded parts.
You simply plug in the diagnostic tool and begin reading the scan tool data. Most scan tools come with cd's or manuals to give you a good knowledge base for beginner diagnosis.
obd 2 scan tools like the Actron 9180 have really come down in price. And reading scan tool data has become much easier thanks to the OBD two standardized protocol. If you learn how to read and use a scan tool on your own car you can use the same exact technique on any car 1996 and up. My advice is to be the envy of your neighborhood and teach yourself how to read scan tool data. Service engine soon lights pop on all the time because the systems are so sensitive. Why not be the go to guy for when this common problem occurs? Reading through my other pages on my auto scan tool homepage is a great place to start. Help this Automobile website grow with a  Custom Search Do you want to talk to a mechanic about reading scan tool data? Need quick professional answers to check engine light questions? This next link takes to a few more articles I wrote on the check engine light problems subject. Go from reading scan tool data back to auto scan tools Learn more about me and this automotive and car repair website on the Auto-facts homepage and find the answers to your car questions
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When your check engine light comes on, and you connect your OBD two scan tool, in most cases you will just be retrieving the code and identifying the system the failure is in. 
The obd 2 scan tool is very easy to use. In most cases you will find the OBD connector just left and below the steering column. 
