GMC 2001 Sonoma Owner's Manual page 77

2-6
When a new vehicle is delivered, the dealer provides
the owner with a pair of identical keys and a key
code number.
The key code number tells your dealer or a qualified
locksmith how to make extra keys. Keep this number in
a safe place. If you lose your keys, you'll be able to have
new ones made easily using this number. Your dealer
should also have this number.
This vehicle has one
-
double sided key for the
ignition and door locks. It
will fit with either side up.