Garmin GPS error & USCG 'Consumer Safety Defect' Report

I have a Garmin GPSmap 172c GPS installed and connected to a Raymarine ST4000 autopilot.

When the GPS is operating properly, it outputs a sequence of NMEA navigational data every 2 seconds. This NMEA data is used by the autopilot to steer a course to a waypoint. However, there is a problem with the Garmin software in that every day at 23:59:59 GMT, it will no longer transmit the NMEA information reliably. Sometimes the NMEA data stops entirely and other times it becomes quite erratic and is transmitted at 8 second, 20 second or some other random interval. When this happens, the autopilot displays a ‘No Data’ warning message and then steers the boat on the last valid course that it received. This behaviour continues until 00:08:34 GMT at which time the GPS reverts to the normal 2 second transmission interval.

I also have 2 Icom radios (M502 and M802), both of which are DSC capable and have a Lat/Lon display. When they no longer receive valid NMEA position information, the Lat/Lon display flashes, alternating between the last valid position received and a series of question marks. This is another indication that the GPS error is occurring.

I’ve been in contact with Garmin about this problem and sent them NMEA log files that showed the error occurring. (Software is available for Macs that will display the NMEA data in real time as it is being transmitted.)

After reviewing these log files, Garmin’s Technical Support department acknowledged that it is a problem in their software. The issue was forwarded to their Software Engineering department in November of 2006 and I was told that a fix would be provided in 2 weeks. When the 2 weeks passed, I was informed that it would be another month and when that passed, Garmin said that they didn’t know when a fix would be available. I’m still waiting for them to fix the problem.

When the GPS stops transmitting the NMEA navigational information, the autopilot maintains the last heading that it received. If that heading happens to be for example, a 30 degree course correction, then the vessel will be steered off course by 30 degrees until it starts receiving valid NMEA data again. I think that this represents a significant hazard and so I cannot rely on the GPS to maintain an accurate course.

I have notified the U.S. Coast Guard and submitted a ‘Consumer Safety Defect Report’ to them. I don’t know if they will pursue a recall or just some kind of advisory but this issue needs to be resolved one way or another.

The Garmin GPSmap 172c is running the latest firmware version which is 2.60, dated May 9, 2006. On the Garmin download site, the firmware for the GPSmap 172, GPSmap 178 and GPSmap 178c also have that same date for their latest updates. I’m trying to find out if this error also affects these units.

Is anyone else using any of these Garmin GPS units and if you are, do you get intermittent navigational errors with them?

(Mac users can download the GPSUtility software to display the NMEA data as it is being transmitted.)

There is an ongoing discussion here regarding this issue and it appears that the problem is more widespread than I originally thought.

Everyone using a Garmin GPS may want to look into this and post your findings if possible.

On May 10, 2007 Garmin released updates for a number of GPS units that fix this NMEA transmission problem.

Here is a list of the affected units:

GPSMAP 178 Sounder
GPSMAP 178C Sounder
GPSMAP 188 Sounder
GPSMAP 188C Sounder
GPSMAP 198C Sounder
GPSMAP 238 Sounder
GPSMAP 298 Sounder
GPSMAP 398 Sounder
GPSMAP 2006/2006C
GPSMAP 2010/2010C

Hello John,

Thanks for the software update and staying on the case. Turns out I have the 2006 and they are sending me an update card for my unit.
Best to you
Mark Giegel


Hi Mark,

Good to hear from you and I hope things are going well with your BCC projects. I’m pleased that this NMEA problem has been finally resolved and that you’re getting the current version of the 2006 firmware.

I have identified another problem and submitted it to Garmin. It’s not as serious as the NMEA issue but, nevertheless, I would like to see it fixed.

The following text is what I’ve submitted to Garmin:

This problem affects a Garmin GPSmap 172c running software version 2.80.

To describe this problem more thoroughly, I will reference the PDF version of the owner’s manual for this GPS (Garmin part number 190-00321-00 Rev. B ). On page 58 of the owner’s manual, the illustration of the tidal page data shows the current time as 09:07AM and the current tide height as 0.7FT. The intersection of the vertical Current Time bar and the horizontal Current Tide Height bar shows the status of the tide on the tidal graph.

The problem with the GPSmap 172c is that when the tide tab is selected from the main menu, the current time box does not always show the correct time. Sometimes it does and sometimes it does not. I have to some extent determined when this problem occurs and how it can be consistently reproduced.

This problem seems to depend upon when the GPS is powered on.

If the GPS is powered on between 12:00:00Z and 23:59:59Z and the tide tab is selected from the main menu, then the Current Time is correctly set to the local time and the Current Time and Current Tide Height bars are displayed correctly. The Current Time will increment correctly and the bars will automatically follow the graphical display. The display will continue to operate properly even if the day changes over to the following day, as long as the GPS is not powered off.

If the GPS is powered on between 00:00:00Z and 11:59:59Z and the tide tab is selected from the main menu, neither the Current Time nor the Current Tide Height bars will be displayed. If the cursor is moved into the graphical tide chart area, then the Current Time and Current Tide Height bars will appear and The Current Time box will default to 12:00. The time can be manually changed by moving the cursor.

The behaviour can be affected somewhat by changing the Time Format setting from the Setup menu. If the Current Time bar is being displayed properly then changing the time format from 12 hour or 24 hour format to UTC will cause the the Current Time and Tide Height bars to not be displayed on the Tide page. Changing the time back from UTC to 12 hour or 24 hour format will restore the display of the bars.

Conversely, if the Current Time and Current Tide Height bars are not being displayed correctly, then setting the Time Format to UTC will cause them to be displayed.

Basically this means that the GPSmap 172c tidal display will operate correctly under local time only if the GPS unit is powered on between the hours of 12:00:00Z and 23:59:59Z.

The problem also existed in software versions 2.60. Perhaps earlier versions also had the problem but I have not verified this. Lastly, this problem does occur on GPSmap 172c units other than just the one that I own.

Here is the response that I received from Garmin re the tidal display problem:

Thank you for contacting Garmin International.

I did receive your email and forwarded it to our engineering department. There response was short and to the point. This is something that is being worked on for the next software version for the GPSmap 172.

This announcement is for any BCC owners who also happen to be Mac users. Come to think of it, all BCC owners should be Mac users because Macs are the BCCs of the computer world:-)

I develop software professionally (Apple only… sorry), and wanted to let you know that iGPS version 2.1.0 has just been released.

iGPS is an easy-to-use Mac OS X utility for backing up and restoring Garmin GPS waypoints and routes. It works with any Garmin GPS that uses a serial interface.

Get more information and download it from the iGPS website.