For the past few weeks, the ability to send directions to your Garmin GPS device via Google Maps have been failing.
A Google Maps Help thread has dozens of complaints from Garmin and Google Maps users.
Garmin has this as a documented feature for sending locations from Google Maps to Garmin devices. But the number of complaints shows that it really does not work.
Daniel from the Google Maps team just replied a day or so ago saying they are working on the fix. He wrote:
Thanks for the reports, we're looking into the issue. I'll post an update here when I have news, stay tuned.
There is no ETA for the fix.
Forum discussion at Google Maps Help.