1995 Cadillac DeVille Owner's Manual - Page 75

The square key is for the ignition only. It has a resistor pellet which is part of the vehicle's PASS-Key I 13' system. The oval is for the doors and all other locks. When your new Cadiilac is delivered, the dealerremoves the plug from the door key. The plug has a code on it that tells thc dealer ora qualified locksmith how to make extra keys. However, the ignition key does not have the knockout plug. The ignition key has a bar code tag attached to it. Your dealer or qualified locksmith, by reading the bar code tag, can then make your ignition key.