Q7 outside temp reading

[nh7571]

Hi, all new to this but need some help, recentley my Q7 has started giving a false outside temp reading, it's reads correct for the first few seconds after start up then falls to anywhere between -5 and 5 degrees, have tried replacing the temp sensor behind the front bumper but no different, I beleave there is a second sensor used (as a comparison and the lower reading is used) but have no idea where it's situated, my question is has anybody come across this? And any idea where the second sensor is? Thanks.