I have what I think is a Symphony II+ in my 2007 Audi A4 Avant. I need to disconnect the battery to clear out the drain hole underneath - is this stereo 'smart-coded' or will it go into SAFE mode? I have a code (from the manual) but have no idea how to input it as nothing I've read on the internet (hold down scan +rds, use radio preset buttons etc.) seems to correspond to the buttons on my stereo. Any advice gratefully received.