here is a better write up than mine for calibration:


This is just what i was going to suggest next. Force the nav to recalibrate.

To do so:
Disconnect the nav by unplugging it completely. Wait until the nav powers down (red LED off) before unplugging. Wait 1 or 2 hours then reconnect.

The waiting time makes sure that the nav looses its almanac data and forces a recalibration.

To calibrate the nav observe the following:

Calibration After Install
After the first install of a nav unit, you must do 3 key actions to calibrate the nav.


Download Almanac
If the GPS almanac is not loaded, the nav is using default orbital data to determine what satellites should be visible. It can take longer to acquire a satellite fix when the almanac is not loaded. Almanac is lost when battery disconnected, and loaded automatically as follows:
Park the car outside, with the tailgate closed so the GPS antenna is not obstructed. Wait around 10 to 15min for the GPS almanac to be updated. You can observe the Almanac status in the service mode by selecting GPS, then Functions then GPS-Tracking info.

Calibrate Gyro Compass
The ignition should be in position 0 (off) during removal and replacement of the nav unit. After installing, close all doors, sunroof, bonnet and tailgate. A bus line reset will be carried out within two minutes. Resetting allows the gyro to perform a calibration run. Do not move or bump the car during this reset / calibration period. After a few minutes the calibration will be complete.


Calibrate Speed Pulse
If the speed is not calibrated, you will notice the nav is inaccurate and doesn’t always track the roads correctly.
Speed is constantly checked and calibrated, but it’s best to do a special calibration run after fitting the nav to ensure it works well for you straight away, as follows:
Take the car for a drive where you can travel over 50kmph, preferred is around 100kmph, for at least 5min steady speed. This will help the nav system calibrate the vehicle speed pulses against the calculated GPS vehicle speed.
To assist the map calibration, you should drive a few right-angle bends. Every time you take a corner, the nav re-corrects the map position to the calculated GPS position. Taking a number of right-angle corners gives the nav a number of points with which to fine-tune map and GPS position

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Vehicles:

1. 2005 4.8is X5 Sapphire Black Metallic/Black Leather, fully loaded (Nav, Comfort Seats, Rear Climate, Sliding Load Floor, Heated Front and Rear Seats, Aux In)
2. 2004 3.0i X5 Jet Black/Black Leather (Lemoned)
3. 1999 Saab 9-5 Turbo (Trade In/Retired)


My Custom X Page (Pics of my 4.8is)