GMC Yukon Denali 2010 Manual page 19

Auto Start
The vehicle also has an Auto Start feature. The engine
will remain off while in Auto Stop mode until vehicle
conditions require the engine to run. The near-instant
starting of the engine from Auto Stop mode is called
Auto Start. Some of the vehicle conditions that may
cause the engine to Auto Start are:
The hood is opened.
The gear selector is in M (Manual Mode).
The hybrid battery state of charge is too low.
The hybrid battery voltage, temperature or power
limits are exceeded.
A remote vehicle start has been requested.
The engine is not at operating temperature.
Acceleration demands require the use of the
engine.
EV Mode
The vehicle also has an Electric Vehicle (EV) mode
which uses only the electric motor to move the vehicle.
With light acceleration, the vehicle will drive in EV
mode. EV mode is unavailable when the vehicle is
out of fuel.
If increased acceleration is required, or the vehicle
reaches approximately 40 km/h (30 mph), the engine will
start automatically. The engine shuts off at speeds
below 40 km/h (25 mph) unless the transmission is in
M (Manual Mode) or Auto Stop is disabled.
During heavy acceleration, both the engine and
hybrid electric motors supply power. A sensation
similar to a transmission gear change can be felt as
the transmission changes modes. Engine RPM may
remain above 4,000 RPM for a longer period during
hard acceleration.
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