Unable to Install Map Update on Nuvi 2599

Does Express see the card? If not I'd reformat the card, note needs to be FAT32, and try again.

Windows File Explorer sees the card. How do I tell whether Express sees it? I don't see any selection in Express Settings that would enable me to determine whether it sees the card. Also, no selection that would enable me to reformat the card. The card has worked fine for the last 5 years, so presumably it's FAT32.

I'd try the steps at https://forums.garmin.com/apps-software/mobile-apps-web/f/garmin-connect-web/61920/garmin-mass-storage-setting-and-changing-it-out-of-mtp-mode and see if that will fix things.  There are two modes of transfer for nuvi devices and you have to have the correct one, otherwise Express won't see the device, but Windows will.  You can format the card by right clicking on it while in Windows Explorer.  Having said that, I would suggest you hold off on that option until it becomes a last resort.  Do you have another card you can try, something 8 GB or more (max = 32)?  

That link is very useful for looking into .System the way a developer would, but it seems to stop short of the "goal" - so what is the other transfer mode, and what do you actually have to do to switch to that mode? Also, why would Express have seen the device for years in the "incorrect" mode, yet suddenly stop being able to do that with the latest map update? I'm with you on holding off reformatting the card until last resort, but I don't have another card that I can try in its place. Btw, is backing up my Nuvi files just a matter of copying all the files from the Nuvi to my PC, or do I need some special software to make sure it's done correctly?

BY following the procedure, you can switch between the two modes.  The 2599 uses MTP and by taking it out of Auto Detect you can force MTP.  Then, if GE connection is established, you can switch it back to Auto Detect.  Some people report the device being in an incorrect mode, and not knowing why or how it got changed.  See https://www8.garmin.com/manuals/webhelp/nuvi2509-2609/EN-US/GUID-B7DC540A-8430-430F-8E4E-6C70EFBBE062.html 

By the way are you attempting the update on a laptop or desktop?

Ah, got it - the "switch" is taking it out of Auto Detect, thereby enabling me to see the files in .System. (I was thinking the procedure was supposed to enable Express to see the card when, for some reason, it wasn't able to do that.) But after following the procedure, I get the same results (not enough memory), so it looks as if I'll have to resort to reformatting the card. I've been trying to do the update on my Windows 10 desktop, though, so maybe I should try my Windows 11 laptop next before giving up.  Btw, the procedure seems to have done something to Garmin Connect. Now I only get a blank screen when I try to go to that site from my desktop.  (Or maybe I screwed up that link by deleting what I thought were nonessential files in the app data.)

No luck on the laptop (same memory issue), but Express seems to have more info & options in Windows 11. For example, there's a "Back Up Now" option that I've never seen in Windows 10, and the Device Storage & SD Storage are clearly displayed, so I don't have to use Windows Explorer to get that info. I do have a 4GB SDHC card in my camera, but it's too wide & thick to fit in the Nuvi slot.

Those options like backup and space considerations are there in Windows 10 but a device has to be connected and they are accessed through the "Advanced" option. Since you aren't connecting that may be the reason the choices are not appearing. But from that you have learned something in that t connection doesn't seem to be completed in Windows 10 but is completed in Windows 11. As I recall, only map files are installed on the card. The balance of the needed files are on the device. Since you can "see" the device on Windows 10, go in and delete the unused voice files and language files.

Another thing to check is what is termed Selective Suspend. This is a power saving feature on Windows 10 laptops and likely on Windows 11 as well. I'm not sure about desktops. Try the suggestion below to determine if they improve your performance.

1. Disable the USB Selective Suspend feature globally within Windows
a. Click the Start button and type edit power plan in the Windows Search box.
b. Click Change advanced power settings
c. Scroll down to USB settings and click the little plus next to USB selective suspend setting to expand the options. Set both the On battery and Plugged in settings to Disabled then click Apply and OK to save changes.

By the way there are basically two physical size cards, the "SD" (SDHC and SDXC) and microSD. The Garmin takes a microSD, the laptop uses SDHC. The microSD card you are using may have come with an adapter that converts the pin and physical size to that of an SD card, thus allowing it to be read in a computer that only accepts SD cards.

I had already deleted the unneeded voice and language files and some other stuff on the device, thereby freeing up about 100 MB, but apparently the essential (and presumably undeletable) system files still take up about 93% of the memory. I went ahead and disabled the USB selective suspend settings on both the desktop and the laptop, then tried the map update again, but still get the insufficient memory message. One interesting development: When I look at the Nuvi via Windows 11 Explorer on the laptop, I can no longer see the SD card. With the Nuvi back on the desktop, the card shows up as a separate drive with a 1.8 GB Disc Image File. Unless that file somehow "contains" the maps, I see no map files on the card -- just lots of free space. My hunch is that the way Garmin now deploys the map updates simply overwhelms the mere 6.8 GB internal memory on the Nuvi 2599 -- regardless of the available space on the SD card -- and I'll be forced to buy a newer model that has much more internal memory.