Circuit Description

Navigation System (USA)

How the Circuit Works
The navigation unit and the navigation display unit are the main components of the navigation system. These two components communicate with each other through the GA-Net II communication bus. The GA-Net II communication bus is also used by the Navigation Display Unit to communicate with the Audio Unit. The navigation unit generates the screen graphics, and then passes them to the navigation display unit as Red, Green, and BLU (RGB) color signals, and a sync signal. The Navigation Display Unit uses Liquid Crystal Display (LCD) and a touch sensitive resistive membrane screen.

Diagram 156-4:

System Diagram

Power Supply
Fuse 7 (in the under-dash fuse/relay box) is hot at all times and supplies battery voltage to the navigation unit and to the navigation display unit.

With the ignition switch in ACC (I) or ON (II), battery voltage is applied through fuse 32 (in the under-dash fuse/relay box) to the navigation unit and to the navigation display unit.

User Controls
A navigation system can be controlled in three ways; (1) voice commands, (2) hard button inputs, and (3) touch screen inputs. The hard button and touch screen input information is communicated to the navigation unit from the navigation display unit via the GA-Net II communication bus. If, for any reason, the GA-Net II communication bus connection to the Audio Unit is open, the hard button and touch screen functions will be disabled. So, when adding accessories, the Audio Unit Connector B must be reconnected per the accessory instructions.

The microphone in the roof console located near the map lights picks up the driver's voice commands. When the TALK switch on the steering wheel is pressed, the voice command is compared with a library of stored voice files in order to find a match. Most of the navigation, stereo sound, and HVAC functions can be controlled with voice commands. When the voice control system is in use, all of the speakers are muted. Refer to the Navigation System Owner's Manual for a list of valid voice commands, or use the voice control system and say, "Help" at any screen. Voice command help on the "Information" screen provides a brief tutorial.

Navigation Function
The navigation system utilizes the GPS signals obtained by the GPS antenna and the vehicle speed signal from the PCM to get a user from a starting position to a destination position. The GPS signals and the vehicle speed signal determine the position of the vehicle icon on the map. The navigation system relies on DVD maps and points of interest (POI) in order to provide the user with the optimum route between starting and destination positions.

Route Guidance
When in route to a destination, the navigation system provides turn-by-turn map and voice guidance. The stereo sound system outputs the navigation voice guidance prompts to the front speakers. During navigation voice guidance prompts, the normal stereo sound signal to the front speakers is muted while the rear speakers continue to play.

GPS Signal Reception
The GPS signals obtained by the GPS antenna are provided by 24 or more satellites in orbit around the earth. The navigation unit supplies the GPS antenna with 5 V through a coax cable to power the antenna's amplifier. The GPS receiver in the navigation unit receives the amplified GPS signals back through the same coax cable. The GPS receiver identifies the satellites and processes the different GPS signals. These signals are then converted to actual locations by the navigation unit in order to determine the position of the vehicle.

NOTE: Rear metallic window tinting or loose items sitting on the rear shelf can block GPS signal reception entirely. Any electronic accessories such as cell phones, PDA's, radar detectors, vehicle locating devices, or audio components near the navigation display, GPS antenna, or control unit can interfere with the operation of the system, and should be disconnected prior to troubleshooting.

Muting
The audio unit orchestrates all muting logic. All voice commands are broadcast over the front audio speakers. The priorities of the other audio inputs are as follows: The Navi voice, the audio unit CD/DVD or AM-FM-XM music channels. The navi signal to mute the radio is sent to the Audio unit over the GA-Net bus.

Navigation Sub Display Unit (Upper display)
The audio unit controls the audio, climate, and time data displayed on this device. The time is updated by the navigation unit, and can be adjusted in the navigation "setup" menu.

Trip Computer
The PCM passes the fuel pulses, and status of the fuel level on the F-CAN bus. The system uses the speed pulses and fuel information to calculate estimated fuel economy. The fuel economy may disagree with actual fuel consumed, and customer estimates based of pump refill records - this is normal.