A GPS receiver compares the satellite time signals to a similar clock in the receiver itself. The satellite clocks measure time by seconds within weeks from 0 to 1023. When that happens, some systems could lose track of time. That means that they will mistakenly think the satellite is billions of miles away instead of 12,000 miles away. According to the receiver's calendar, the signals would have left space 19 years ago.
Nothing goes wrong with the satellites.
The problem is with receivers back on Earth getting confused because of the wrong date. Hikers or weekend yachters should check with their manufacturers. Renenger says every GPS system that was ordered through Air Force channels has been fixed. The GPS industry has known about this problem for years, says Peter H. Dana, a GPS designer who teaches computer cartography at the University of Texas. Therefore most people who need GPS to find directions will be fine.