It could be that the smb connector on the nav unit was badly secured and was not giving a good signal, it could just be one of them things, gremlins

Welcome to the forum BTW.

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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.