The PATS module is a white box with 2 sets of wires being plugged into it located under the drivers dash way behind the fuse box. If you unplug it you will not get your expy started.
On the pats module you will find a part/serial number and you keypad password. Its also what recieves input from the keyless entry. Its a complicated system and im currently finding a way around it. Been locked out of my 01 expy too many times now