From the Avalanche site:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">And I did finally figure out the keypress combo to activate the diagnostic menu--first off, nav disc must be loaded in order to actually access any of the diagnostic options. With disc loaded, press the "Nav Rpt" button, then press and hold the "Config" button for around 10 seconds until the diag screen appears. At the "Navigation Check" main menu, press the "Back" button onscreen in order to access the submenu (titled simply enough, "Menu") shown in the first picture in this reply. Pressing "Debug" apparently overwrites part of the nav map display with numerical data...sorta like some sort of screen dump. I didn't really try to mess with some of the other options for fear of possibly making my nav no longer function, especially after I was foolish enough to press one of them--next thing you know, the nav was constantly plotting location strictly based on GPS signal (the GPS symbol was constantly displayed), and my clock no longer displayed the correct time zone offset.
Other notes:
On the GPS Information screen (the one which lists the satellites), I figured out what some of the fields represent--the numbers next to the 3D, 2D, and NG stand for the number of seconds the GPS was in that particular mode (3D--meaning at least 3 satellites; 2D for 2 satellites; and NG for no signal). Pressing the Edit softkey allows you to adjust the clock.
On the Vehicle Sensors screen, I was able to confirm that the speedometer is pretty much dead-on accurate; the pulse count increases while your vehicle is in motion...it resets to zero when you exit out of the Vehicle sensors screen. </div></BLOCKQUOTE>