I just had that problem. Your temperature sensor wires are no longer attached to the ambient temperature sensor. What you are seeing is the two extremes when the two wires make and break contact. If you look, you'll probably see the wire hanging down around your driver's side front wheel well/brake duct.
The fix may be as simple as reconnecting the wires to the sensor. Or that may be gone as well (it was in my case), so you'll need to purchase a new one and reconnect it. (About 40 bucks.) Be sure to get the connector as well. (About 5 bucks.)