nuvi 2559 [C4 or not] are really no different than most nuvi models in method to reach preboot but all 2xx9 can be notoriously difficult to work with. Generic instructions are detailed in the link given above by catymag. If the unit's not bricked it's much easier to update firmware from media card or use WebUpdater etc with gupdate.gcd. If you're trying to patch firmware for unlocked maps, there's a kit for SD flashing available in this post: [Only registered and activated users can see links. ]. It's for both HWIDs of 25x9. Just firstly read the edit behind the spoiler and make the region change for the nonvol backup from 41 to 154 in Update.txt file.