Well I did some poking around and found on the 2007 navigation unit if you hold the channel preset buttons 3 and 6 down at the same time it will go into diagnostic mode.

If you hold it too long it will go all the way to the speaker test. If that happens just hit return.

If you go to the GPS button (lower left) it tells you what's happening and how many satellites you're getting.

In a good area I had 8 satellites. When there are lots of trees the number shrinks.

Bob