Displacement On Demand (Dod); Automatic Transmission Operation - GMC 2005 Envoy Owner's Manual

Displacement on Demand (DoD)

Your vehicle's engine may be equipped with
Displacement on Demand (DoD). This system allows
the engine to operate on either four or eight cylinders,
depending on your driving demands.
The system determines when to switch into and out
of the four-cylinder mode by first making sure that
certain enabling criteria are met, such as coolant and
oil temperatures, and the transmission being in
either THIRD (3) or FOURTH (4) gear.
When greater power demands are required, such as
accelerating from a stop, passing, or merging onto
a freeway, the system will maintain eight-cylinder
operation. When less power is required, such a
cruising at a constant vehicle speed, the system will
automatically enable the four-cylinder mode, allowing
your vehicle to achieve better fuel economy.
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Automatic Transmission Operation

There are several different positions for your gear
shift lever.
PARK (P): This position locks the rear wheels. It is
the best position to use when you start the engine
because your vehicle cannot move easily.