Lexus service said my XM antenna was interfering with my nav system (same description you gave affected me), so they relocated the aftermarket xm antenna further away. Problem solved. Good luck!

 

my XM antenna is located at the rear of my GX inches away from the rear spoiler. not sure where yours was located. i never really had a problem like this and as i mentioned earlier it sort of corrected itself.

 

Solar flares cause of GPS problems?

http://www.cnn.com/2011/TECH/mobile/...tml?hpt=hp_bn7

 

Somehow you are not getting a GPS signal to your NAV system. I had my dashboard replaced and then I had the same problem. After I "aligned” the GPS the way that was described in this thread my GPS would work well for a few days, but sooner or later, I would be off in the ocean. (I live in Florida) The problem is that there is no GPS signal. This is probably due to the antenna becoming disconnected. It is almost impossible to figure out where the disconnect is located. There is a connection right behind the touch screen and there is another connection in the back of the "Computer" under the passenger seat. I would check the one under the passenger seat first. That one is easy to get to... All you have to do is unbolt the seat. Getting behind the NAV screen is not hard either. Just look up GPS hack and there are step by step directions on how to remove the screen. My guess is that a connection got loose. At least that would be the easiest solution.

The reason your GPS seems to work after a calibration is because it has the ability to track roads based on tire speed and cardinal direction. It only works for a while because this mode is not very accurate. It is designed to work this way for when you lose GPS signal for a short period, lets say a tunnel or a parking garage.

Reseat those GPS antenna connections and you may find that it will work.

Let me know if you have any questions.

 

Just got new app for my Iphone4 its called GPS DRIVE MOTIONX FOR $19.99 YOU WILL GET one year of voice guidense.