From the 2001 through 2005 model years, Dodge Neon cars used a 4-button remote with FCC ID GQ43VT9T. Plymouth Neon vehicles also used this remote until Plymouth ended production after the 2001 model year. This keyfob had several different Chrysler part numbers, but the current manufacturer part number for it is 04759008AF.
Programming the system in your vehicle to accept a new remote requires that you already have one working remote. If you do not have a working remote, you will not be able to program the system yourself, but will have to take it to a dealership for programming.