If you have a Samsung Galaxy S3 and you aren’t getting a GPS lock and a GPS icon does not show in the notifications area when using an app that uses GPS (e.g. Google Maps or GPS Status & Toolbox). Try the below.  Worked for me on an AT&T S3 (stock 4.1.1 rooted), not sure about other models/carrier versions:

  1. Dial *#197328640#
  2. Select [1] UMTS
  3. Select [6] Common
  4. Select [6] NV REBUILD
  5. Select [1] NV REBUILD
  6. Wait 30 seconds
  7. Reboot phone