GMC 1998 Sonoma Owner's Manual page 69

Side Access Panel (Extended Cab)
(If Equipped)
Your
vehicle may be equipped with a side access panel
for convenience in loading and unloading cargo.
To open the side access panel, first open the driver's
front door. Then, use the handle on the panel to open
it.
You must close the side access panel before you can
close the driver's door.
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.
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