GMC 2007 Envoy - Manual (Page 129)

Torque Lock
If you are parking on a hill and you do not shift
your transmission into PARK (P) properly,
the weight of the vehicle may put too much force
on the parking pawl in the transmission. You
may find it difficult to pull the shift lever out
of PARK (P). This is called “torque lock.”
To prevent torque lock, set the parking brake and
then shift into PARK (P) properly before you
leave the driver’s seat. To find out how, see
Shifting Into Park (P) on page 127.
When you are ready to drive, move the shift
lever out of PARK (P) before you release the
parking brake.
If torque lock does occur, you may need to have
another vehicle push yours a little uphill to
take some of the pressure from the parking pawl
in the transmission, so you can pull the shift
lever out of PARK (P).
Shifting Out of Park (P)
Your vehicle has an automatic transmission shift
lock control system. You have to fully apply
the regular brakes first and then press the shift
lever button before you can shift from PARK (P)
when the ignition is in RUN. See Automatic
Transmission Operation on page 118.
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