GPS/Nav performance problems

I recently bought a 2002 M3 with the navigation system. But its performance has been far poorer than expected.
On any cloudy day and many sunny ones, the GPS has no idea where I am.
I always get a lat/long reading, but the nav's map places me miles from where I am and often shows me offroad.
Is this normal? Or should the GPS work on both sunny and cloudy days, and even rainy ones too?
BTW, I definitely have the correct CD installed (Pennsylvania), but no prior experience with GPSes.
Thanks,
Randy
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Randy wrote:

You don't carry anything on your rear deck/parcel shelf do you?
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GPS can handle the normal weather conditions you describe. Insure there's nothing obstructing the antenna. Don't know if the BMW system has a data page which indicates the ID and number of satellites being tracked, but that's the only way you can insure the antenna side is working properly. It takes 4 satellites to get a precise solution.
R / John
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John Carrier wrote:

Does the owner's manual say anything about the screen displaying an icon when it is receiving a satellite signal? Also, if you have aftermarket window tint, perhaps it is metallized which would interfere with satellite signal reception.
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greg wrote:

There is such an icon on the display, and it very rarely indicates that GPS is operational. Oddly, GPS sometimes places me correctly on the map even when the icon indicates that it should not.
No obstructions on the rear shelf. No special window tinting (AFAIK).
I called the BMW service rep who worked with me to replace the nav trunk unit earlier. He suggested that it may just need some "codes" reset. Supposedly the nav unit is still covered by the two year parts warranty. So I guess I get to visit another BMW dealership...
Thanks,
Randy
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Randy wrote:

AIUI when you update the software, that is "coding". Maybe the antenna is not properly plugged in. You can get magnetic GPS antennas from ebay for not very much money so you could try using a new one and see if there's any difference. With the magnetic ones you can stick them on the outside of the car (temporarily) to get a clearer route tothe satellites.
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