Navigation System: Description and Operation

NAVIGATION SYSTEM

CIRCUIT OPERATION

The following components make up the navigation system:
- Navigation Computer (Z289)
- GPS Antenna (Z292)
- Display and Control Unit (Z291)

Navigation Computer (Z289):
The Navigation Computer (Z289) is located in the right hand side of the luggage compartment, attached to a bracket. The Navigation Computer (Z289) is the main component in the navigation system and receives input from the BECM (Z238) and the GPS Antenna (Z292). The Navigation Computer (Z289) contains a solid state piezo gyro which measures the motion in the vehicle around its vertical axis. The gyro operates on the principle known as the Coriolis force (Refer to the workshop manual for detailed operation).

Using the inputs from the BECM (Z238), the GPS Antenna (Z292) and the gyro sensor, the Navigation Computer (Z289) can determine the vehicle s current position, direction and speed.

The Navigation Computer (Z289) also houses the CD-ROM drive. This drive is used to read map data from country specific CD's and also to load updated software into the computer.

GPS Antenna (Z292)
The GPS Antenna (Z292) is located underneath the air intake plenum and is connected to the Navigation Computer (Z289) via a single co-axial cable and passes signals received from the GPS satellites to the Navigation Computer (Z289) for processing.

It is possible for the antenna to lose the signals from the satellites in hilly or tree lined areas, built up areas with tall buildings, multi-storey car parks, garages, tunnels, bridges and during heavy rain/thunderstorms. When the signal is lost, the navigation computer will continue to give guidance using memory mapped data from the CD map until the signal is restored.

Display and Control Unit (Z291)
The Display and Control Unit (Z291) is located in the centre of the fascia. The unit comprises of a colour Liquid Crystal Display (LCD) screen and controls to operate the navigation functions. The Display and Control Unit (Z291) comprises four control switches, one rotary press menu control and one status LED. A photosensor is used to control the brightness of the screen in day and night time conditions (Refer to the workshop manual for detailed operation).

Diagnostics Mode
The navigation system may be put into a on-board diagnostics mode (service mode) by selecting the "settings" menu from the main menu then pushing and holding the menu key for about 10 seconds. The service mode has four main functions:
1. To check that components are fitted and to determine their hardware/software levels.
2. To perform a quick "health check" of the major input signals to the system.
3. To check for correct operation of the display and control unit keys.
4. To check the status of the GPS reception.

Selecting the on-board monitor item from the service mode menu causes the version info to be displayed. The screen displays the software and hardware level of the display and control unit together with the diagnostics and bus index. The supplier of the unit is also displayed as a number code defined by BMW. The system queries the display and control unit before displaying the information on the screen. If the unit responds with Software Hardware levels this implies that the component is connecting to at least power, ground and K-bus.