Dale DePriest - first published 99/1/4/99 - revised 00/5/30
There are several undocumented commands available, primarily at startup, on Garmin handheld receivers. This article will attempt to document some of the features available. I will try to document these in a universal way although details may differ depending on the unit you have. There are variations among models and among software releases within models. There is no attempt to provide 100% mapping to a particular model or release. Instead I have used a "try it" approach. I have documented what you may see and you will need to verify exactly what you did see. You may wish to print this out and check mark the features that are applicable to your unit.
Note that these features are not documented by Garmin for a reason. They are generally for testing the device and are not intended for end users. The modes are not supported by Garmin and may cause you to lose data in your machines. Try this at your own risk!
One major feature that is revealed when using these undocumented test modes is that there is a thermometer inside your Garmin unit. The intent of this thermometer is to compensate the internal time-of-day clock for changes in temperature which will cause the internal crystal to drift. To a lesser extent it is also used to adjust the contrast of the display screen for temperature changes. It will not measure ambient temperature except when the unit is first turned on since the internal temperature is changed due to the heating effects of the electronics in the unit. The thermometer based correction works by building a table of correction values that are then applied to the internal clock. This is only used to obtain an initial fix since after the fix the satellite data is used to keep the clock accurate. Similarly while you have a fix the accurate clock can be used to update the temperature data in the table which means the unit will compensate for aging parts and even the complete loss of the table.
The three keyboard keys on the right side of the unit have special significance if held down while powering on the unit. These keys are generally called page, mark, and enter. On the GIII units the center key is call menu but for our purposes it behaves the same. On Street Pilots the equivalent keyboard names will have to be used. These are page, option, and enter. See below for etrex and emap startup sequences.
On some units this feature has been documented in the manual and will offer a warning message before erasing. However, some versions of software, even on these machines, do not offer the warning. Do not depend on the documentation here. Have everything of value backed up before trying this. The big plus of this feature is that this reset can fix problems with the unit that will avoid having to send it back to Garmin.
Note that setting back to factory defaults means everything. You will not only lose things that you can backup but also settings that you cannot. For example the user defined datum, the user defined grid, any preferences and datums that you have set up, any customization of any kind. The leap second data will be gone. The Garmin waypoint will reappear if you have erased it. You will not have any of the tuning that was performed to calibrate your unit at Garmin so expect poor initial lockup performance. You will need to have a clear view of the sky and recollect a full almanac. This takes about 15 minutes.
The test mode screen can appear automatically if the unit detects a failure during power up. You can use this mode to verify certain operations of the unit. For example hitting each key will cause the corresponding key in the display to darken. Hitting the enter key twice in a row (on some units it is the page key) will cause a graphic pixel test which could highlight any bad pixels in your display. Hitting the same key again will further test the display. Hitting the key one more time will return to the main test screen. One units that use the page key to perform this test you can use the quit key to perform the graphic test backwards. The power/lamp key will show both an indication and actually light the lamp.
Other displayed entries are specific to internal tests performed in final test but the temperature (in Celsius), the internal and external battery voltages, and the gps time can be useful. On the G-III+ and 12Map this mode will also display the version number of the software which has been removed from the start up screen. On some units status of the power on diagnostics can be viewed here.
Hold the "up" and "enter" keys and then press the "on/off" button to reset the entire machine. You will receive a warning prompt.
This may be the most useful of the secret modes available on Garmin handhelds and for some the hardest to access. Basically you start the Garmin normally by pressing the power button and while the opening screen is being display you must press each of the 4 arrow keys once in any order. If you accomplish this feat you will be rewarded with a quick switch to the status screen without waiting for the rest of the time-out. You should notice a -.- just under the satellite display to confirm your success. If it doesn't work then power down and try again. It takes a certain rhythm to be successful. This will not work on G-III or G-III+ units but most of the information is available on these units in normal mode. On G-II and G-II+ units this method will only work if you have the unit set in portrait mode. The etrex and emap do not support this mode.
The beauty of this mode is that you can leave the unit in this mode while using it. It adds a new Diagnostic menu item and more information in some of the displays.
The diagnostic page content will vary depending on which unit you have but will generally contain diagnostic pass/fail messages at the top of the screen, the elapsed time for the unit, internal software information, and finally battery voltage.
Pressing quit will return you to the normal screens of the gps but realize the gps continues to work fine while you are looking at the diagnostic screen. If you hit goto or mark you will perform these functions.
It is worth mentioning a little about the elapsed time meter. Generally this is expected to be the time since the last factory reset. However, it will be reset by the power-on/mark key sequence described above and it may be reset by some software upgrades.
On some units the battery voltage includes both internal and external voltages. The internal voltage is indicated in .03 volt increments and seems to have this accuracy. The external voltage is indicated with the similar precision but does not have this accuracy. The external voltage has the following decimal setting for each whole voltage setting: .14, .29, .43, .57, .72, .86, and .00.
On some units, mostly older multiplex units, you can redisplay the world globe that appeared on the opening screen. Change to the map page and then hit the power-off button but stop before holding it down long enough to power the unit down. The globe will appear and you can control the speed of its spinning using the arrow keys.
Has anybody found any more?
Dale DePriest