GMC 2001 Sierra 1500 Pickup Owner's Manual page 90

There are several ways to lock and unlock your vehicle.
You can use the keyless entry system (if equipped).
You can also use your key.
To lock the door from the
inside, slide the lever
rearward. To unlock
the door, slide the
lever forward.
Power Door Locks (If Equipped)
Press the recessed side of the switch marked "U" to
unlock all the doors at once.
If your vehicle has this
power door lock switch,
press the raised side of the
switch, marked "L" on
either front door to lock
all the doors at once.
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