Instruments - Compass Loses Calibration
SI B 51 14 04Body Equipment
November 2004
Technical Service
SUBJECT
Digital Compass Looses Calibration
MODEL
E53 X5 Sports Activity Vehicle from 5/04 and equipped with Interior Mirror with Digital Compass (Option 4NA)
SITUATION
Customer may complain of the digital compass on the interior rear view mirror:
^ Displays wrong direction on long trips.
^ Locks in only one direction.
^ Displays "C" (in Calibration mode).
^ Misses one or more directions (not showing all directions).
CAUSE
The digital compass can loose calibration if:
^ Large Electromagnetic Interference is present. For example: when driving very close to Power Lines, Subways, Steel Bridges, Car Washes, Metal Salvage Yards, High Steel Buildings, etc.
^ Vehicle has been relocated to a different zone variance.
^ Compass was calibrated incorrectly or in the presence of a strong magnetic field.
INFORMATION
The digital compass displays the direction of where the car is heading and it is capable of distinguishing 8 primary directions: North, North East, East, South East, South, South West, West, and North West.
All compasses measure readings relative to Magnetic North direction. The difference between Magnetic North and True North varies from place to place across the surface of the earth. Different parts of the earth are separated into numbered "Zone Variance" (see map). Therefore, the digital compass must be set approximately where it is on the earth's surface so that the Magnetic North reading can be properly converted into a True North display. Entering the Zone Variance number in which the compass operates completes this calibration process.
Although the digital compass is securely protected from changes in magnetic field, it still can be susceptible to large changes in magnetic field. Examples include, but not limited to: high tension power lines, large steel buildings, subways, steel bridges, automatic car washes, large quantities of scrap metal, etc. While infrequent, an occurrence of this phenomenon is possible.
During normal operation, the Digital Compass electronic will continuously update and adjust for gradual changes in the vehicle's magnetic remnant field. If the vehicle is subjected to high magnetic influences, the compass may display false reading, locked direction or unable to be calibrated. If this occurs, perform the calibration procedure. On long trips, a vehicle may leave its original zone and enter one or more new zones. Generally, if no more than 3 or 4 zones are temporarily driven across, there is no reason to recalibrate the compass or reset the Zone Variance. Only when the vehicle is permanently relocated to a new zone, the compass must be calibrated in the new Zone Variance. Each zone is approximately 4.20 wide. A typical driver will not notice any difference on the compass display until a total of about 22.50 zone is driven across. At this situation of driving more than 22.50 zone wide, a reading can be off by one or more primary directions.
The correct zone variance must be verified and the compass must be recalibrated if the compass continuously displays incorrect, erratic or locked reading.
ZONE VARIANCE MAP
PROCEDURE
1. Verify the customer's concern.
2. Move the vehicle to an area away from large metallic objects or overhead power lines.
3. Check and adjust Zone Variance for the correct geographic location (See Zone Variance Map). Hold the reset button located on the underside of mirror (1) and release when the zone number appears in compass window (2). Press the reset button (1) again to correct the zone. Display will automatically return to normal.
4. Press the reset button (1) until "C" is displayed in the compass window (2).
5. Once "C" is displayed, the vehicle must be driven (with windshield wipers off) in at least 2 complete 360° circle at a speed of less than 5 miles per hour.
6. Continue to drive the vehicle in circles until the "C" is replaced with the correct direction. Up to 3 complete 360° circles may be required.
7. The compass is now calibrated and should operate normally.
8. Repeat this calibration procedure if the compass continuously displays incorrect direction, the reading is erratic or the display is locked.
WARRANTY INFORMATION
Information Only.