Join Date: Jan 2007
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Welcome to the forums. It sounds like either the exterior sensor or the wiring to it at fault. The sensor is the small "dimple" that will be at the base of one of the wing mirrors. To access it you will need to remove the mirror glass. Also I think the wire can fray where it passes through the trunking between the body and the door. Not sure on sensor prices but they should not be much.
Currently in dave_mezza2006's garage:
2014 Vauxhall Astra Limited Edition 1.4 16v VVT Turbo