OBD2 will give you some limited fault code identification and virtually no 'live' engine running information.[/b]
Not quite- it all depends on the software you are using with the interface. OBDII was orignally intended to aid with diagnostics in the combustion process. It can reveal far more than just fault codes. For example, I have a copy of Proscan which I can use to view and record live data on (to name but a few)
Manifold pressure
Air Mass
RPM
Coolant temp
Intake air temp
Ignition advance
Short & long term fuel adaptation
etc etc
However what it cannot do is alter any values or programme any functionality. Fault code reading is also limited to the fuel system.
This is where Tech II comes in. Apart from being able to read fault codes from all the other systems (airbags, ABS, TCS, transmission, electrical etc etc ) it can also be used to programme functionality such as deadlocking options, alarm beeps, ACC and so on plus the important security elements. Furthermore the TechII reader itself acts as an interface for TIS2000, which is a PC based application that offers far more diagnostic control.