So far i dont have this prob with my D6.
only my compass is unable to calibrate due to my own mistake. i accidentally bring my D6 into MRI room with 1.5T magnetic field strength... arrrggghh...
For your case, there are 2 possibilities. the first one, the temp sensor already "kaput" or defective. you can identify this by changing the unit to imperial and observe the value changes.. Second possibility, something wrong with the software. Need to reload the software again. In both cases, you need to send back your dive comp to Suunto authorize dealer or directly to Suunto finland.
good luck