Another issue I'm having with my HHR is the shifter (auto) locks in park and it takes several tries to get it to shift.

 

Search function at the top of the page - search for "shifter locked" - lots of info available.

 

Kind of rare on your model year, but probably has soda type fluid spilled inside of shifter causing the mechanism to stick.

 

Probably the lever of the knob is not reaching/pushing the "plastic shaft" to make the changes. You would disassemble and add and spacer between. I had the same issue too and this fixed it.

 

x2
I have it a couple of months ago. Damned Fanta spilled.
The problem was solved with the help of Mr. Whopper and spray WD.
I just removed the cover of selector, found stopper (small white plastic element) and sprayed it.