Dept. of Homeland Security: Your old GPS might not work after April 6

Your old GPS might not work after April 6 © Peter Janssen

If you're cruising anywhere on or after April 6, you might want to check your GPS, particularly if it's an older one. It might not be working.

The problem is what is called a Global Positioning System Week Rollover Event on April 6. If your GPS is not designed to handle the rollover, it might revert to an earlier year, in which case it would not be able to calculate your position accurately. This situation should not appear with relatively new GPS devices, but it could appear in older models.

The issue is severe enough that the Department of Homeland Security recently issued a warning about it. Here's what DHS had to say: "GPS devices with a poorly implemented GPS Time-to-UTC conversion algorithm may provide incorrect UTC following a week number rollover. Additionally, some GPS devices that calculate the week number value from a device-specific date rather than the start of the current GPS Time Epoch may provide incorrect UTC at some other device-specific date."

All this revolves around the timestamp from satellite signals that GPS uses to calculate positions. Timing started on Jan. 6, 1980. The system stores the week number using ten binary bits, counting from zero to 1,023, which represents about 20 years. Every 1,024 weeks the counter rolls over and starts again at zero. That happened in 1999, and it will happen again on April 6.

The system relies on a GPS to UTC, or universal time, algorithm to provide the correct time and therefore location. Devices with a poor (meaning out-of-date) algorithm won't work after the rollover on April 6.

Older devices may need an upgrade or a patch to work. DHS recommends that you contact the manufacturer of your GPS to make sure the proper updates have been installed.

For its part, Garmin said that "Our devices that were produced after 1998 should not be affected. And if they end up being affected then we will address the issues as they appear. But again, the rollover should not affect our devices after 1998."

To read more:

• www.the-triton.com/2019/02/gps-users-warned-of-potential-april-6-glitch
• www.theregister.co.uk/2019/02/12/current_gps_epoch_ends
• ics-cert.us-cert.gov/sites/default/files/documents/Memorandum_on_GPS_2019.pdf