To access some Garmin GPS (global positioning system) maps, the user must enter a code to unlock them on a Garmin GPS receiver. City Navigator and BlueCharts are two map types that must be unlocked. If you receive a "Can't Unlock Maps" message on the GPS device when you power it on, you can remedy the situation by following a few simple steps.
Create an account at the MyGarmin website (see below). Enter your e-mail address and other information, and then follow the on-screen instructions to create your account.
Register your device. Click on the "myProducts" tab and then on the "Register" hyperlink. Follow the instructions to add your Garmin GPS device to your account.
Return to the myGarmin home screen by clicking on the tab marked "Home." Click on "Manage Maps & Downloads" and then on "Details" next to the GPS device for which you'd like to unlock the maps.
Click on "Add maps with product key/coupon code" and then click either "On the Road and Trail Maps" or "On the Water Maps." Type the product key or coupon code that came with your map purchase in the area labelled "Unlock Information." You may be prompted to enter the serial number too. Click "Unlock Map" and the map will be unlocked.
View your unlock code from the "Manage Maps & Downloads" area. Click "Details" next to your GPS device and scroll down to the unlock code. You can copy the code into the Garmin software if prompted.