Chevrolet 2007 Colorado Owner's Manual page 120

ON (C): This is the position that the switch
returns to after you start your engine and release
the switch. The switch stays in ON when the
engine is running. But even when the engine is
not running, you can use ON to operate the
electrical accessories and to display some
instrument panel cluster warning and indicator
lights. The transmission is also unlocked in
this position on automatic transmission vehicles.
The battery could be drained if you leave the key in
the ACC or ON position with the engine off. You
may not be able to start your vehicle if the battery is
allowed to drain for an extended period of time.
START (D): This is the position that starts the
engine. When the engine starts, release the key.
The ignition switch returns to ON for driving.
When the engine is not running, ACC and ON
allows you to operate the electrical accessories,
such as the radio or items plugged into the
accessory power outlets.
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A warning tone will sound if you open the driver's
door when the ignition is in ACC or LOCK and
the key is in the ignition.
Key In the Ignition
Never leave your vehicle with the keys inside, as it
is an easy target for joy riders or thieves. If you
leave the key in the ignition and park your vehicle,
a chime will sound, when you open the driver's
door. Always remember to remove your key from
the ignition and take it with you. This will lock
your ignition and transmission. Also, always
remember to lock the doors.
The battery could be drained if you leave the
key in the ignition while your vehicle is parked.
You may not be able to start your vehicle after
it has been parked for an extended period
of time.