Look on the inside of the trunklid for a Service Parts Identification Label. It has a list of RPO (Regular Production Option) codes. You can google for a GM RPO decoder.

For example, the codes for a '98 are:
AU0 Lock Control, Remote Entry
A90 Lock Control, Rear Compartment Lid
Remote Control Electric Release
UA6 Theft Deterrent System

Then use this link to program the new fob-- http://www.grandprixforums.net/how-p...fob-53653.html