Cadillac 2005 STS Manual page 12

To make your name selections easier, the system will
only allow you to select a character which can follow the
last one entered. For example, if you enter Z, you
would not be allowed to follow it with T. The system will
highlight the available characters and darken the
unavailable characters.
If you are unsuccessful when inputting a name, it may
need to be selected differently. It is also possible that the
map DVD database may not contain that information
or the correct search area has not been selected.
See Database Coverage Explanations on page 2-66
for more information.
The following screens are some of the different alpha
keypads you will have access to:
2-4