Why is my Blackberry keep shutting off every two minutes when I am using mobile phone GPS for my car?

I use my BlackBerry for GPS in my car. I use Google Maps for the navigation. Normally when I drive, the screen always stays on. Today, the unit started shutting off every two minutes (the maximum power saver setting). Why is my Blackberry keep shutting off every two minutes when I am using mobile phone GPS for my car? What could be causing this? What can I do to fix it? I have tried taking the battery out for thirty seconds (twice). I also deleted and reloaded Google maps. But nothing worked. Please help. Thanks.