GMC Yukon 2007 Owner's Manual page 146

Your vehicle has a Computer-Controlled
Cranking System. This feature assists in
starting the engine and protects components. If
the ignition key is turned to the START position,
and then released when the engine begins
cranking, the engine will continue cranking for a
few seconds or until the vehicle starts. If the
engine does not start and the key is held in
START for many seconds, cranking will be
stopped after 15 seconds to prevent cranking
motor damage. To prevent gear damage, this
system also prevents cranking if the engine is
already running. Engine cranking can be
stopped by turning the ignition switch to the
ACCESSORY or LOCK position.
Notice: Cranking the engine for long periods
of time, by returning the key to the START
position immediately after cranking has ended,
can overheat and damage the cranking
motor, and drain the battery. Wait at least
15 seconds between each try, to allow
the cranking motor to cool down.
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2. If the engine does not start after 5-10 seconds,
especially in very cold weather (below 0°F or
−18°C), it could be flooded with too much
gasoline. Try pushing the accelerator pedal all
the way to the floor and holding it there as
you hold the key in START for up to a
maximum of 15 seconds. Wait at least
15 seconds between each try, to allow the
cranking motor to cool down. When the engine
starts, let go of the key and accelerator. If
the vehicle starts briefly but then stops again,
do the same thing. This clears the extra
gasoline from the engine. Do not race the
engine immediately after starting it. Operate
the engine and transmission gently until the oil
warms up and lubricates all moving parts.
Notice: Your engine is designed to work with
the electronics in your vehicle. If you add
electrical parts or accessories, you could
change the way the engine operates. Before
adding electrical equipment, check with your
dealer. If you do not, your engine might not
perform properly. Any resulting damage would
not be covered by your vehicle's warranty.