PRE 99 - Get in the vehicle and close all the doors

- Turn the ignition on & off quickly (no more than 3 seconds) to start the process. Next, Take the first key - hold down button #2 (unlock) while striking button #1 (lock) three times. Release button #2. Confirmed by door lock operation. 

- Repeat for second key within 30 seconds of first. 

- After last key then cycle the ignition on/off to finalize the process 

For vehicles 99 and later (diamond shaped key) the procedure is identical except you hold the LOCK button down while 
pressing the UNLOCK button 3 times.