GMC 2001 Sonoma Owner's Manual page 79

There are several ways to lock and unlock your vehicle.
You can use the keyless entry system, if you have this
feature. You can also use your key to unlock your door
from the outside. To lock your door from the inside,
slide the lever on the inside of the door down.
You can also use the power door lock
switch (if equipped).
2-8
To unlock the door, slide the
lever on the inside of the
door up. You will see a red
area on the lever.
Power Door Locks (If Equipped)
If your vehicle has power door locks, the switch is
located on the armrest. Remove the ignition key and
press LOCK to lock all the doors at once.
To unlock the doors, press the raised area next to the
key symbol.