Either the GPS antenna or the GPS module, try the antenna first, it's the cheapest, approx EU10 of ebay (any SMB female plug should be fine).

What car is that in, I've not seen the temp displayed there before??

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Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.