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 many of 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 and some other 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. Other Garmin units typically have some of these special modes as well although the key sequences may be slightly different. I have documented some of them below.
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 re-collect 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. Some units report a Bravo Version which is the version of the hardware. On some units the status of the power on diagnostics can be viewed here.
While not obvious to an observer the test mode also starts the interface to emit PVT solutions in Garmin mode on units that support PVT output. Once started, this mode will continue even after a power off until you change it in the interface section by selecting "none". The fact that this command sets Garmin mode may be useful for other purposes as well. For example this may be a way to recover from a bad software load or even a corrupt map load.
The etrex also has secret modes for test purposes. Hold the "up" and "page" keys and then press the "on/off" button to enter this screen. It behaves similar to the test mode described above and shows some information that is useful to the user. Note that is has been reported that the ROM test may show a false failure on this screen since a factory tester is not attached. You can run the key tests by pressing each of the keys. You can use the page key to cycle through all of the display tests. The screen shows the status of the power on diagnostics plus internal battery voltage and external if present. A clock display shows seconds, the revision level of the software is shown, and a thermometer reading shows the internal temperature in degrees Celsius.
Hold the "up" and "enter" keys and then press the "on/off" button to reset the entire machine. You will receive a warning prompt. You can avoid this message using the sequence "Page" plus "Enter" plus "Up" and then press the "on/off" button. Hold the keys down for 5 seconds to perform the reset.
The newer etrex units (venture, legend, and vista) with the "Click Stick" use different keys to accomplish these tasks but the idea is the same. Holding the click stick down and then powering up will enter the test screen while holding the "page" key down and the "click stick" down and then powering up will reset the unit. You will be prompted with an "are you sure?" message. On these units holding down the "find" button in addition to the others will avoid the "are you sure" message. Hold the buttons for 5 seconds to clear the unit.
Note that the extra key sequence may be an even bigger master reset but this is not clear to me. A master reset may be needed to clear the unit if you have left the batteries out for a long period of time and the unit comes up with the wrong year. Later versions of the firmware have supposedly addressed this problem. To continue after a reset click here.
The Legend CX can be forced to Auto Locate by holding down the upper zoom key while powering up. I suspect this feature is common to several unit.
To totally reset this unit with firmware prior to 2.20 hold the Zoom Out and Quit buttons down and then press the power on. All user data will be lost as will the almanac. To continue after a reset click here. Garmin, in its wisdom, has decided to disable the reset feature so there is no current way to reset the unit.
Otherwise the standard secret keys apply. To continue after a reset click here.
The reported method to completely reset on of these units hold the "menu" key and the "quit" key down and then press the "power on" key. Hold for a full 7 seconds and then release. As with the other units all information will be lost and you will need to reload the almanac and all your saved user data to make the unit usable.
For the 76S try this sequence to master reset it. Press and hold quit, Menu, and the rocker down key. Then press and release the power on key. release the rocker down and wait for the welcome display. Now release the quit and menu keys.
Otherwise the standard secret keys apply, including the 72 model. To continue after a reset click here.
A newer units come out Garmin seems to continue to find new sequences to try and fool the user. In some cases they have removed the reset features completely claiming that they can cause problems and mask problems that need to be fixed. As always use these at you own risk.
On units without a reset sequence Garmin provides a way to set every setting back to factory defaults.
The Geko uses the OK key instead of an enter key. It enters test mode by holding OK and pressing power on. The master reset can be accomplished by pressing all the keys except the down key for 5 seconds. To continue after a reset click here.
Hold enter while powering up to enter test mode. Hold enter and page while powering up to master reset the unit. The 76C and 76CS should use the same key strokes as they use the same firmware. To continue after a reset click here.
The reported reset sequence is press and hold the zoom out button + the Nav button + the Quit button and then tap the power button. Continue to hold the zoom out + Nav + Quit button until the unit comes on. This will reset the GPS 176 C to the factory settings. This reset will erase all user data like waypoints, routes, etc.
Also note the sequences in the 76 section above which may have some information for some 176 models. To continue after a reset click here.
If you have to perform a full reset using one of the sequences shown above you will need to allow the unit to collect a full almanac before normal can be resumed. First a fix will need to be obtained which can take from 5 to 10 minutes of leaving your unit outdoors, stationary, with a good sky view. After the first lock you will need another 12.5 to 15 minutes to get the almanac reloaded. Check the date to insure that the information was reloaded properly. Time will be shown as UTC time since your local time offset was lost in the reset.
Re-establish all of your preferences such as time zone, daylight savings flag, etc. Reload all your waypoints and saved routes from your backup. I do hope you have a backup. WAAS capable receivers will have to re-establish the WAAS almanac as well.
This may be the most useful of the secret modes available on some of the older Garmin handhelds and, for some users, 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.
The III+ can display some icons that are not available on the icon menu. These are usually found in a downloaded map. For example the geographic place names are not available except when shown on the map. However you can use a trick to get these icons into you own waypoints. Find an entry using one of these waypoints on the screen and then press enter to convert it to a waypoint. You can now edit the waypoint values and name to be whatever you wish. These new icons will probably not be preserved when saved on a pc and re-entered since the pc program may not support them.
On the etrex models with the click stick you can reach an internal diagnostic message page which reports stack data and shutdown data. First change to the trip computer page and press the "zoom out" key, the "zoom in" key, and the "zoom out" key once again. This will turn on the diagnostic reports page.
In some other units the diagnostic reports can be reached from the trip computer page by pressing the cursor keys, up, right, down, and left in sequence. This is reported to work in the 60C and probably will work on the 76C as well.
Once your on the diganotic screen the page key will switch to a screen that shows the condition of the last few shutdowns.
Has anybody found any more?
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first published 99/1/4/99
added etrex 00/5/30
add emap 00/6/2
added III+ icon trick 00/7/5
added new etrex models 01/4/9
added 76 and alternate keys for etrex 01/12/22
added V reset 02/03/09
added paragraph on reset recovery 02/07/17
added 72, Geko. 03/03/10
added Legend CX 07/04/05 auto locate