The OBDII scanner resets the codes. Many aftermarket parts stores have similar programs. They are hoping that after you get the code you buy A part from them. BTW, OBDII =on board diagnostics generation 2. This A standardized mandatory diagnostics system required by all manufactures who sell in the States. You can buy A scanner that will pull the codes on everything from A Kia to A Bentley for under $50 US. There are other manufacturer specific codes it will not read, but these will not cause the Check Engine Light to come on. It's the law.

The code list should be easy to obtain. Do A search. I'll try to post A link later. Keep in mind that just because you get A code for running lean that A MAFS ( mass air flow sensor )may not rectify the problem. Many other things can cause this code. IE ; fuel pressure, restricted air filter, software glitches, etc. Another example, A code for A bad temperature sensor may actually be because of A low coolant level or the computer needs A updated PROM.

Here is A link to some basic OBD info http://www.flatratetech.com/pub34.htm

Here is A link to the list of generic codes http://www.obdii.com/codes.html