Automatic Transmission Operation - GMC Sierra 2000 Owner's Manual

Automatic Transmission Operation

There are several different positions for your shift lever.
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If your vehicle is equipped with an automatic
transmission, it features an electronic shift position
indicator within the instrument cluster. This display
must be powered any time the shift lever is capable of
being moved out of PARK (P). This means that if your
key is in OFF, rather than LOCK, there will be a small
current drain on your battery which could discharge
your battery over a period of time. If you have to leave
your key in the ignition in OFF for an extended period,
it is recommended that you disconnect the battery cable
from the battery to prevent discharging your battery.
PARK (P): This locks your rear wheels. It's the best
position to use when you start your engine because your
vehicle can't move easily.