>>What more would the home built code reader do for me?>>
It would get you to the MAIN Modules CODE storage banks.
The one you are using [ built-in ] accesses ONLY emmissions codes ..
which trigger the CE lamp.
If you really want to know whats up with your car, you don't want only emmissions codes , you want Systems Management codes. Which are accessed at the other sockets.
http://www.peachparts.com/shopforum/showthread.php?t=107630