Mine too, asked almost the same question last week, nobody knew, well nobody answered.
Mines been reading between -3 and -10!!
My mechanic says they are under the front bumper and are always getting knocked and giving erratic readings. He said they are just for the ice warning/temp display and arent connected to the ECU.
Hope he's right!
Edit: just doing some fishing on the net, and apparently its in the nearside mirror! But also apparently prone to going haywire.