I have the same problem. Mine will show either -38 degrees or -44 degrees. I took it to the shop and they could not replicate the problem. I asked them to order me a senson an replace it. $75 later, I still have the same problem. I spoke to the service manager and he's trying to find the answer.
By the way, I have the same problem another poster mentioned about the tire pressure sensors, too. I've replaced three of them in the two years I've had this car.