Cadillac 1998 DeVille Owner's Manual page 74

The square key is for the
ignition only. It has a
resistor pellet which is part
of the vehicle's
PASS-Key% system.
The oval key
doors and all
is for the
other locks.
When a new vehicle is delivered, the dealer removes the
plug from the door key. The plug has
a
code on it that
tells the dealer or a qualified locksmith how to make
extra keys. The ignition key has a bar code tag attached
to it rather than a knock out plug. Your dealer or
qualified locksmith can make extra ignition keys by
reading the bar code tag.
Keep the bar code tag and the door key plugs in a safe
place. If you lose your keys, you will be able to have
new ones made using the plug or bar code tag.
NOTICE:
Your vehicle has a number of new features that
can help prevent theft. You can have a lot of
trouble getting into your vehicle if you ever
lock your keys inside and you may have to
damage your vehicle to get in. Be sure you
have extra keys.
2-3
\ .