Interesting. The Alldata for a 2011 shows it to be on the frame rail right side. I'll have to check mine for location.

 

I think Mitchell shows it in the lower grille hole, which would be strange since they usually have the same errors. For instance the RCDLR location.

My Mitchell only goes to 2010 it shows it on the horn.

But I have proven to myself that it is in the lower grille on my 2011.

 

This is a picture of my sensor in my 2011 red hhr.

 

Checked mine today on the 2011 and it is behind the grill lower left side just like donbrew said. It is not on the right side frame rail. 2011 Alldata is wrong.

 

If you want to include photos in a post you will have better success doing it this way:
https://www.chevyhhr.net/forums/how-...ur-post-52643/