Chevrolet 2010 HHR Owner's Manual page 149

If you are parking on a hill and you do not shift into
P (Park) 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 P (Park).
This is called torque lock. To prevent torque lock, set
the parking brake and then shift into P (Park) properly
before you leave the driver seat. To find out how, see
.
Move the shift lever out of P (Park) 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
P (Park).
This vehicle is equipped with an electronic shift lock
release system. The shift lock release is designed to:
Prevent ignition key removal unless the shift lever
is in P (Park) with the shift lever button fully
released, and
Prevent movement of the shift lever out of
P (Park) unless the ignition is in ON/RUN or
ACC/ACCESSORY and the regular brake pedal
is applied.
The shift lock release is always functional except in the
case of a an uncharged or low voltage (less than 9 volt)
battery.
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