I've had it rise some sitting in traffic but went back to normal once I got moving again.
The sensor is prolly dead, its located at the front of the car below the hood latch, its a little black probe about 2" long.
Good thing you still got warranty to cover the parts
You may have some electrical gremlins in the car Jim, if various sensors are going out or acting funny. Is your alternator over charging?
don't know for sure, but my battery did drain out a couple weeks ago - i disconnected my Trunk box and it has been fine since. had the battery checked out and it was deep cycle charge/tested and good to go.
i plan on taking it in and i will mention to them to check the alternator also.