According to everything I can see...both the service manual and the parts manual...the 1999 Grand Prix did not have a Passlock system. There was an option for content theft security systems, something I'd expect a GTP came with from the factory.
There are no instructions for programming keys, the OEM key sells for about $9...a Passlock key sells for almost $30, and the ignition lock cylinder case sells for under $100. One with Passlock...the sensor is in the case...usually goes for a minimum of $200.
