Chevrolet 2010 HHR Owner's Manual page 150

If the vehicle has an uncharged battery or a battery with
low voltage, try charging or jump starting the battery.
See
To shift out of P (Park):
1. Apply the brake pedal.
2. Then press the shift lever button.
3. Move the shift lever to the desired position.
If you still are unable to shift out of P (Park):
1. Fully release the shift lever button.
2. While holding down the brake pedal, press the
shift lever button again.
3. Move the shift lever to the desired position.
If you still cannot move the shift lever from P (Park),
consult your dealer/retailer or a professional towing
service.
3-38
for more information.
Before leaving the vehicle, fully press the clutch pedal
down, move the shift lever into R (Reverse), and firmly
apply the parking brake. Once the shift lever has been
placed in R (Reverse) with the clutch pedal pressed
down, the ignition key can be turned to LOCK/OFF, then
remove the key and release the clutch pedal. See
Things that can burn could touch hot exhaust
parts under the vehicle and ignite. Do not park
over papers, leaves, dry grass, or other things that
can burn.
.