1. Close the vehicle doors.
2. Insert key in ignition and turn to ON (As far as you can without cranking engine)
3. Turn ignition OFF and remove the key from the ignition.
4. Press and hold the driver side door lock switch in the UNLOCK position.
5. Insert the ignition key into the ignition lock cylinder and remove the key. (Do not turn the ignition key in the lock cylinder.)
6. Insert the ignition key into the ignition lock cylinder and remove the key. (Do not turn the ignition key in the lock cylinder.)
7. Insert the ignition key into the ignition lock cylinder. (Do not turn the ignition key in the lock cylinder.) Leave the ignition key in the ignition lock cylinder.
8. Release the door lock switch. The vehicle will sound three beeps in order to verify the Program Mode has been activated.
9. Press the LOCK and UNLOCK buttons together on the keyless entry transmitter and hold until the vehicle beeps twice to verify that the transmitter has been successfully programmed (this take approximately 15 seconds).
10. Perform the previous step to program up to four transmitters (including your old ones).
11. Remove the ignition key in order to exit the Program Mode.
Someone sent the following instructions for 1999 Century. If you have trouble with the first set of instructions try these.
1. Sit in the driver's seat
2. Remove the ignition key from the ignitionn lock cylinder
3. Close all the doors
4. Press and hold unlock on the door lock switch (on the door)
5. While holding the door lock switch in the unlock position, insert and remove the ignition key TWICE. DO NOT TURN THE KEY IN THE LOCK CYLINDER ... JUST SLIDE IT IN AND BACK OUT.
6. Insert the ignition key the third time, leaving the key in the ignition cylinder. DO NOT TURN KEY
7. Release the door lock switch. You will hear 3 chimes indicating the transmitter programming is active.
8. Press and hold the lock and unlock buttons on the keyless entry remote at the same time for 12 seconds.You will hear two chimes.This indicates the transmitter has been pogrammed.
9. Repeat step (8) for all additional transmitters to be programmed
10. Exit programming by removing the key from the ignition cylinder.