No need to buy the unit unless you are all out DIY'er.However as I just posted on an OBD2 thread.this site has tons of great info on engine diagnostics,codes,and how to track down what the code is potentially trying to tell you,all FREE.
A great read,some night when you have nothing to do and want to learn up on how systems operate.
ohlord
AutoTap - OBDII Diagnostic Scanner
join their email list and they sent out a great news letter full of info......