GMC 2006 Sierra - Manual (Page 120)

Automatic Transmission Operation
If your vehicle is has an automatic transmission, it
features an electronic shift position indicator within the
instrument panel cluster. This display must be powered
anytime the shift lever is moved out of PARK (P).
See Fuses and Circuit Breakers on page 5-123.
There are several different positions for your shift lever.
See “Range Selection Mode” later in this section.
PARK (P): This position locks your rear wheels. It is the
best position to use when you start your engine because
your vehicle cannot move easily. If your vehicle has the
Allison Transmission
® , with the Power Takeoff (PTO),
use PARK (P) when starting. The Allison Transmission ®
has a park pawl that is designed to hold the weight of
commercial medium duty trucks. Therefore, the Allison
Transmission
® uses larger parts than other automatic
transmissions. These larger parts may sometimes make
a clunk noise when the selector lever is moved from
DRIVE (D) or REVERSE (R) to PARK (P). This is normal
and there is no damage occurring during these shifts.
When parked on a hill, especially when loaded, you may
notice an increase in the effort to shift out of Park. See
Torque Lock (Automatic Transmission) under Shifting
Into Park (P) (Automatic Transmission) on page 2-53 for
more information.
Automatic Transmission
Allison Transmission ®
2-26