[ImperialCrown]

If it happened during a jump start while the battery was failing or during a battery replacement, a voltage spike may have occurred and froze the logic of the thermometer. I would first try another battery disconnect, pause and reconnect to attempt a reset. Reset the clock.
-40°F is the default temperature when the 2-wire plastic ambient temp sensor (mounted under the front bumper and easily hit) is in open circuit.

 

[Bob Lincoln]

Agree that whenever a reading is stuck at one end of the scale, either it needs a power reset or is damaged.

 

[Hankster]

The wires for the ambient temp sensor are routed through a 4 wire plug mounted just infront of the battery mounted on the front crossbar. It is possible that the plug or wires were damaged during the battery replacement.