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Old 01-09-2006, 11:05 AM
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Contributed by: Roland
Steps to troubleshooting GPS problems:

1.Has it been determined yet if the Nav is getting GPS signals? Check the Satellite Icon at the upper right side of the display or go into the maintenance menu and see how many satellites you have.


2. The way the nav operates is that when you turn the ignition off, the 90 seconds it takes for the nav to turn off it is writing data to the non volatile memory on board the Nav, like last position data and other parameters.



3. When the car is re-started the Nav initially quires and loads what was/is in memory because in theory the car has not moved and should be in the last position. If you want to try this with two units, just take them both out of the car and swap them (just make sure they donít have access to GPS signals at start up and they will display the last position where the cars were)This is
why if you unplug power to the nav before the 90 seconds is up the memory is corrupted and it cant figure out what to do and you have to "replace" it.


4. When the Nav does not have GSP signals to navigate, it goes into a mode called "Dead Reckoning". This means that it still tries to navigate with the inputs it has and it still tries to plot the positions (the inputs it still has is the speed sensor and it has an internal gyro for inertial measurements of left and right movements). Though not all that accurate if you are going to rely solely on these inputs to navigate, it can buy you some time because there will ALWAYS be GPS signal drop outs and the nav unit is on its own at these times. This is what happens if you are in a tunnel, high rise garage, tree obstructions, etc. Itís that we as drivers just donít notice it, but this is what is happening.


5. Now if there are no GPS signals for guidance, the inertial sensors take over. As said before, they are O.K. for a while but over time they introduce errors and you stray from the path because thatís all it can do. The nav does not have a GPS update to tell it where it "really" is so it goes on its merry way. Once the Nav gets a GPS update the Nav knows where it is and updates what I will call a "true known position" and you are now back
on track. So this is why a bad antenna can be a bad thing. Also I believe this
is why the guy is a mile off.




As I said before, check to see if you have any GPS signals (go to
the maintenance menu) and if not itís your GPS antenna.



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