We have been towing a 2007 HHR automatic for three years. As stated by other users, you have to pull a 2 amp fuse from the passenger side, centre panel. I found pulling off the panel, then the fuse each time a major pain so I wired in a toggle switch c/w a 2 amp fuse holder. The toggle switch is then mounted on the driver's side, under the dash, where it can be easily reached. I no longer have to remove the panel. The material required, wire, toggle switch, 2 amp fuse holder cost $10.00!
Derek Hudson
PS: The only issue with the HHR is that the tow bar attaches to the front end very low on the vehicle. Even with a 6" drop down receiver, the tow bar is still sloped up towards the motorhome. Although within the 4" allowed, it still has caused excessive, premature wear on my Blue Ox tow bar. I have towed my HHR for only 20,000 miles and am presently rebuilding my tow bar for the second time. I will be adding hitch immobilizers to both receivers which I hope will solve the problem.
