Principles of Operation

PRINCIPLES OF OPERATION

NOTE: The smart junction box (SJB) is also known as the generic electronic module (GEM).

Audio Control Module (ACM)
The audio system can be operated while the key is in RUN or ACC. The ACM sends AC voltage audio signals to the speakers or to the amplifier, depending on vehicle configuration. The ACM can produce its own DTCs, which can be communicated to the scan tool through the medium speed controller area network (MS-CAN), or retrieved through the ACM self-test by simultaneously pressing presets 3 and 6.

The ACM receives the following messages through the MS-CAN:
- Reverse signal
- Received from the parking aid module (PAM) and used for muting the audio output when a parking aid system tone is sounded.

- Vehicle speed signal (VSS)
- Received from the ABS module and used for the speed-compensated volume feature.

Both of these messages are also used by the navigation system to more accurately depict the vehicle location.

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.

Antenna - AM/FM
The antenna is a fixed mast antenna mounted on the exterior of the vehicle. The antenna receives both AM and FM radio waves. The audio signals are then sent to the ACM through the antenna cables.

Antenna - Satellite Radio
The satellite radio antenna is located on the roof of the vehicle. The antenna receives digital audio signals and sends them to the satellite digital audio receiver system (SDARS) module through the satellite radio antenna cable. On vehicles equipped with navigation, a combination satellite radio/global positioning system (GPS) antenna is utilized.

Antenna - GPS
The GPS antenna is located on the roof of the vehicle. The antenna is a combination satellite radio/GPS antenna, even if the vehicle is not equipped with the satellite audio system.

Subwoofer
The subwoofer speakers are powered by the subwoofer amplifier. The enable/clip detection circuit carries out 2 functions: to turn the amplifier on, and to indicate to the ACM when the subwoofer output distortion signal reaches a damaging level. The ACM then clips the audio output signal to prevent damage to the subwoofer.

DVD Entertainment System
The DVD entertainment system utilizes a rear entertainment module (RETM), mounted to the headliner and provides video playback on a screen when a video DVD is played. The audio signals to the rear speakers are routed from the ACM through the RETM. The wake-up signal for the RETM is sent from the ACM through the MS-CAN.

Single-Play Mode
In single-play mode, the audio input from the RETM is broadcast through all of the vehicle speakers. This audio input includes the DVD and peripheral gaming devices plugged into the RETM.

Dual-Play Mode
In dual-play mode, the ACM continues to control the output to the front speakers, while the RETM controls the audio to the rear speakers and headphones.

Satellite Audio
The satellite audio system consists of the SDARS module, a satellite radio antenna, and antenna cable. The satellite radio antenna receives digital audio signals and sends them to the SDARS, where the signals are converted to analog and sent to the ACM (or the RETM, if equipped). The wake-up signal for the SDARS module is sent from the ACM through the MS-CAN.

Navigation
The navigation module is integrated in the ACM and controls the operation and the interface between the user, the vehicle subsystems, and the external components. The navigation ACM 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 ACM calculates route data. The navigation ACM 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 GPS antenna is used to track several available satellites simultaneously. The GPS antenna only receives data - it does not communicate with the satellites. A gyroscope, integral to the navigation ACM, monitors the pitch and yaw of the vehicle created during cornering or turning. Vehicle speed and reverse signals received through the MS-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 ACM monitors the change in reference voltage to determine the requested function.

Audio Input Jack
The audio input jack allows for a portable MP3 player to be connected to the vehicle audio system. When a portable MP3 player is connected, audio from the MP3 player can be played through the vehicle speakers.