Do you have the selection for Postcode? Which Firmware version is on it?
According to [Only registered and activated users can see links. ], with FW 3.60 was this fixed:
Code:
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There is a slight chance that the Nuvi 310 doesn't support this anymore.
In a German forum a user reported this Problem with CN Europe 2011.10 and Germany.
So possible, with the latest maps the Nuvi doesn't support this anymore. Maybe you can check with Garmin