Garmin Memory Cards | What is the largest SD (Secure Digital) card that my nuvi can accept?
From Garmin, 21 March 2012:
As long as the unit has the latest version of software, your unit can use the following maximum card size from the table below.
Unit Series = nuvi series
Maximum Size of SD Card = 32GB
(The following devices will still only support an 8GB SD card during the map update with Express: nuvi 295, nuvi 800 series, nuvi 805 series, nuvi 5000, and zumo 665)
All devices that support SDHC (High Capacity) cards will support up to class 10 cards.
You can use the WebUpdater program at the following link to download the latest unit software version: http://www8.garmin.com/products/webupdater/howtoinstall.jsp
This page from Garmin's web site has additional details:
Frequently Asked Questions