The answer to the OBD2 question is yes and no. The OBD2 will read all of the standard codes related to engine operation and the emissions system because that is required by law. That's the yes part.
However, there are more detailed Porsche codes and many more modules that the obd2 reader won't even access. All those modules, alarm, ABS, airbag, display cluster, transmission, etc, aren't read by the obd2 reader.
There are definitely codes that the obd2 reader won't see, that will kill the car, and won't cause a CEL. For example the alarm module can disable the car in the event of it being stolen, or at least the module believes it is being stolen, that does just what you describe because it turns off the fuel system.
There is a home system that works with a laptop and will show you all of these codes and allow you to access them and reset them. It's sold by durametrics.
www.durametric.com but it's a whole lot more expensive than the scanners. You might be able to find someone on here, or a shop that is close enough to come over and check. The computer stores the codes so even if the car is running they should be able to pull the codes up. The dealer can use their PIWIS or PCT2 terminals to do the same thing.
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