Chevrolet 2009 HHR Owner's Manual page 112

Automatic Transmission Operation
If the vehicle has an automatic transmission, the shift
lever is located on the console between the seats.
P (Park): This position locks the front wheels. It is the
best position to use when starting the engine because
the vehicle cannot move easily.
2-28
There are several different
positions for the automatic
transmission.
CAUTION:
{
It is dangerous to get out of the vehicle if the shift
lever is not fully in P (Park) with the parking brake
firmly set. The vehicle can roll.
Do not leave the vehicle when the engine is
running unless you have to. If you have left the
engine running, the vehicle can move suddenly.
You or others could be injured. To be sure the
vehicle will not move, even when you are on fairly
level ground, always set the parking brake and
move the shift lever to P (Park). See Shifting
Into Park (Automatic Transmission) on page 2-34.
If you are pulling a trailer, see Towing a Trailer
(Automatic Transmission) on page 4-34 or Towing
a Trailer (Manual Transmission) on page 4-41.
Make sure the shift lever is fully in P (Park) before
starting the engine. The 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 the vehicle can shift
from P (Park) when the ignition key is in ON/RUN.