Sometimes a Garmin GPS will become "locked," where a screen prompts you for a pass code before the device will continue to work. This is to prevent someone who has stolen your GPS from using it to find out information such as your home address. Sometimes, however, it can become locked by accident. The only way to obtain a pass code is to call Garmin and prove that you are the original owner of the device. They will then issue you a code that works to unlock your GPS.
Lost Satellite Reception
If at any point your Garmin GPS loses contact with the satellites that provide it information as to your specific location, the device will stop giving you real-time driving updates. This can happen for a variety of reasons. If you are driving through a tunnel or through a hilly or mountainous area, the GPS can easily lose its signal. Be patient and calm. Once you re-enter clear ground the GPS will locate the satellites once more.
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If at any point the maps on your Garmin GPS get accidentally deleted, restoring them is easy to do. Register for an account and log in on the Garmin web page. Select "Manage Maps and Downloads" from the options at the top of the screen. Click on the icon for your registered GPS that comes up, then select "Details" and "Download Again." Plug your GPS into your computer; this will restore all of its original maps and any updated ones you may have downloaded.