I know this is an old post, but has anyone else had this issue? I just started having the same problem, except that it's the opposite. The cooled seat button activates the heat, while the heat button does nothing.
Drove the GT from Atlanta to Lansing, MI for the holidays. Started the trip with 420 miles on the car. I'm sitting at 1466 today.
So far, my MPG is around 25 for the trip with most of the highway miles giving me over 26. All tanks have been 93 octane.
Mine did the same thing early this morning. It popped back up as delivered. I called the dealer and it wasn't there yet but they were able to track it down as on its way.
Hopefully yours is in the same boat!
There is no set fee but the dealer may ask for a deposit. The amount will vary depending on the dealer. Whatever they offer, make sure you get it in writing before handing them a check. Also, make sure the deposit is refundable.