What does the Passlock System actually do?

When the passlock system is activated what does it actually do? I understand it cuts off the fuel system but how does it actually do this?

You might check out the following site:

http://www.standardbrand.com/web_app/viewfiles/viewfilepublic.asp?Current=TechTips&fname=9303_SPED.PDF&fpath=%2Fweb%5Fapp%2Ftechtip%2Fdownload%2F9303%5FS PED%2EPDF++++++++++++

Welcome to AF slampe.

Here is another article that explains these systems and remote starters as a bypass.
http://www.bulldogsecurity.com/pdf/Model721.pdf


and here is a lnk ot GM specific modul.
http://www.the12volt.com/installbay/uploads/FEF_N555L_7-02B.pdf