Unfortunately, the method described at " enabling diagnostics mode on a garmin gps" doesn't work for the Garmin eTrex GPS. To enable diagnostic mode on an eTrex, Hold Up and Page when powering the unit on. You'll get a screen with a lot of information (http://home.wish.net/~marx/etrexd.jpg)

Displays


BRAVO Ver 6            -Operating system version
Software ver. 2.09 -Software version
10:41:09 pm -The time (f course)
temp 27'c -Internal temp
bat 2.94v -Battery voltage
ext--------------v -External voltage(from outside source)????
freq 16368323 -The frequency it's tuned to?????
Drft-------------- -Frequency drift???????
Rdrj-------------- -Rejected? Rejected what?
Sgnl 1671 -Signal strength? It keeps changing.
SNR 0 -Signal to Noise Ratio? It sometimes changes.
BRV pass -Something that was checked passed, but what?
RAM pass -Random Access Memory check passes?
ROM pass -Read Only Memory check passed?
^ 70 () -70 what? has test buttons on both sides.
^ () -More button test icons.
() 994BC6DC - ??????????

Thanks to Dolph Hebb for this.

If you have a Garmin eTrex Legend (and this probably works for the Vista as well), you can enable diagnostics mode by pressing and holding the click stick and turning the unit on. You should see a screen containing information similar to this:

Software Version       2.36
Bravo Version             7
Since Reset      0013:51:23
Time               21:13:48
Temperature              22
Frequency          16368350
XO Drift             ---.--
Signal                 1769
SNR                    0.00
Battery                2.63

After the text, there is a graphical display representing the unit's various buttons. Pressing a button will light up that button's representation on the display (much like calibrating a joystick). There is also a series of shaded rectangles displaying the 4 shades of grayscale the screen supports. By pressing the "Page" button twice, you can flip through a series of display diagnostics (on these screens, the clickstick can be used to adjust brightness and contrast).

Have fun, and if you find any more hidden features, I'd love to hear about them.

In addition to the information presented to you on the device's LCD screen when you enable diagnostics mode the Garmin will also be transmitting test data via the RS-232 port. Plug the GPS device into your serial port via the cable included with the unit (or on the Mac via a USB converter) and then use your favourite terminal application to output the data (on Mac OS X the 'cat' command is perfect).

On my eTrex Legend the data consists of a chunk of data transmitted every second formated in the proprietary Garmin GPS protocol. The chunk of data is actually the machines date and time. Just like the diagnostic info provided via the screen this information of limited use to the average user - but anyone writing software to communicate with the Garmin might have a use for it. I found it useful whilst writing my Mac OS X GPS software (Geode), it was useful for testing the Garmin protocol's lame checksum algorithm.

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