Depending on the length of time the power was interrupted, your system may require GPS initialization.

If initialization is not necessary, the system proceeds directly to the Startup Confirmation screen.
If the system fails to locate a sufficient number of satellites to locate your position within 10 minutes, the following screen is displayed.

If you are experiencing GPS reception problems:
Safe Driving
You can find many safety recommendations throughout this chapter, and
throughout this manual. ...
Safety When Performing Maintenance
Some of the most important safety precautions are given here.
However, we cannot warn you of every conceivable hazard that can arise in
performing maintenance. Only you can decide whether or not y ...