I just got the new navigation system for my car with my iphone 3gs and when i press the “find my location” on google maps it shows that I’m about half a mile from where I actually am. I have no idea how to fix it. I wonder its just a glitch or my gps is broken. Can anyone tell me whats the problem is and how to fix it?

Here's the actual item: Ford Fiesta DVDFord Fiesta Indash Touchscreen Navigation DVD System with Digital GPS

Thank’s