How to flash a computer on a 99 sunfire - 1999 Pontiac Sunfire

The onboard computer requires specialized diagnostic equipment to first read the vehicle identification number stored prior to re-flashing the new program. If the computer is new, the request data command also unlocks the computer to allow the re-flashing of data.
There are a few GM dealers that have "off-board" programming equipment that can re-flash the Power Train Control Module (PCM) at the parts counter, however most will require the vehicle and PCM.
I would recommend having it done at the dealer so you get the most recent software. Usually a 1 hour labor charge, get an estimate prior to having them do the work.
Good luck.