How do you program a 1999 gm venture key fob?

Answer 1

Turn ON the ignition, with the engine OFF.
Attempt to start the engine, then release the key to ON (vehicle will not start).Observe the SECURITY light , after approximately 10 minutes the light will turn OFF.Turn OFF the ignition, and wait 5 seconds.Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the Passlock™ Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).Important: The vehicle learns the Passlock™ Sensor Data Code and/or
password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.Start the engine (the vehicle has now learned the Passlock™ Sensor Data Code and/or password).

With a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles). ( SET AND TURN KEY ON & OFF THIS MANY TIMES AND IT WILL BE CLEARED WITH IN MINUTES )
Be sure to have a battery charger on the car, as this 30 minute procedure may drain the battery to a point were it will effect the programming- or cause a dead battery.
The other way is to have a dealer scanner re-program the system.
DANNY COLEMAN