Principles of Operation
PRINCIPLES OF OPERATIONNOTE: The smart junction box (SJB) is also known as the generic electronic module (GEM).
Audio Unit
NOTE: The audio unit is also referred to as the audio control module.
The audio unit can be operated while the key is in RUN or ACC. The accessory delay feature allows the audio unit to be operated for a preset period of time after the key is moved to OFF and a front door has not been opened. The audio unit sends AC voltage audio signals to the speakers or to the amplifier, depending on vehicle configuration. The audio unit can produce its own DTCs, which can be communicated to the scan tool through the medium speed controller area network (MS-CAN), or can be retrieved through the audio unit self-test by simultaneously pressing presets 3 and 6. The audio unit communicates via the MS-CAN.
Satellite Audio
The satellite audio system consists of a satellite radio receiver, a satellite radio antenna, and an antenna cable. The satellite radio antenna receives digital audio signals and sends them to the satellite radio receiver, where the signals are converted and sent to the DVD player, if equipped, or directly to the audio unit. The satellite radio receiver communicates via the MS-CAN.
Antenna - AM/FM
For sedans, the combination AM/FM antenna is located on the rear window glass. An antenna isolator module is used to reduce interference from the rear window defroster. The audio signals are sent to the audio unit via a coaxial cable. The AM/FM antenna cannot be replaced separately from the rear window glass.
For wagons, a fixed-mast AM/FM antenna is used, rather than an in-glass antenna.
Subwoofer
The Audiophile system is equipped with a subwoofer and subwoofer amplifier. The audio unit controls the subwoofer amplifier through the enable/clip detection circuit. The enable/clip detection circuit carries out 2 functions: to turn the amplifier on, and to indicate to the audio unit when the subwoofer output distortion signal reaches a damaging level. The audio unit then clips the audio output signal to prevent damage to the subwoofer.
DVD Player
When a video disc is inserted into the DVD player and the PLAY button is pressed, an image is displayed on the screen and a stereo signal is transmitted to the audio unit. The DVD player allows for single/dual-play mode. The DVD player communicates via the MS-CAN.
Single-Play Mode
In single-play mode, any audio input routed through the DVD player is broadcast through all of the vehicle speakers. These audio inputs include the DVD player and peripheral gaming devices plugged into the DVD player.
Dual-Play Mode
In dual-play mode, the audio unit continues to control the output to the front speakers, while the DVD player controls the audio to the rear speakers and headphones.
Navigation System
The navigation module is integrated into the audio unit and controls the operation and the interface between the user, the vehicle subsystems, and the external components. The navigation module is on the MS-CAN and can be diagnosed with a scan tool.
The vehicle navigation system guides the user to a pre-entered destination. A navigation map DVD stored in the navigation module sends route calculation data to the audio unit. The audio unit audibly and visually instructs the user of the maneuvers required to arrive at the destination entered.
In order to calculate the initial vehicle position, the global positioning system (GPS) antenna is used to track several available satellites simultaneously. The GPS antenna only receives data and does not communicate with the satellites. A gyroscope, integral to the navigation module, monitors the pitch and yaw of the vehicle created during cornering or turning. Vehicle speed and reverse signals received through the CAN are also used to detect vehicle speed and direction changes.
Steering Wheel Controls
The steering wheel controls consist of a series of resistors. Each steering wheel control switch function corresponds with a specific resistance value within the switch. When a switch is pressed, the audio unit monitors the change in reference voltage to determine the requested function.
Noise Suppression Equipment
The radio frequency suppression equipment reduces interference transmitted through the speakers by the engine ignition and electrical systems. When installing any new radio suppression equipment components, make sure that a good contact is made at all connections.
Network Communication
The following audio system components communicate via the MS-CAN:
- Audio unit
- Navigation audio unit
- Satellite radio receiver
- DVD player
The following messages are utilized:
IDS Scan Tool Acronyms
The IDS scan tool used the following acronyms for modules addressed:
