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Home >> Mercedes Benz >> 2020 >> SLC43 AMG Base >> Repair and Diagnosis >> Electrical >> Motors, Switches, Relays >> Electrical System - Body - 172 Chassis - 2 Of 5 >> Basic Knowledge >> Audio Mode, Function >> Audio Mode, Function - GF82.85-P-2030RDM

Audio Mode, Function - GF82.85-P-2030RDM

Model 172.4 

as of model year 2017 

G13848179Courtesy of MERCEDES-BENZ USA

Shown on model 172.4 

Function requirements, audio mode, general 

General information on the audio mode 

The functions in audio mode are selected using the following controls:

Menu guidance and the display of additional information are carried out on the Audio/COMAND display. The Audio/COMAND display is switched on by the audio equipment via telematics CAN. The picture signals are received by the Audio/COMAND display over the low voltage differential signaling line from the audio equipment.

In vehicles except CODE 810 (Sound system), the audio equipment emits the audio signals at the vehicle's speaker system.

On vehicles with CODE 810 (Sound system), the audio signals are forwarded via MOST to the sound system amplifier control unit, which actuates the speaker system.

The audio mode consists of the following component functions:

Function sequence for volume/tone settings 

All volume and tone settings are performed using the audio equipment. This is performed either by the user or automatically by the audio unit.

The sound settings can be changed with "Tone" and the system returned to the default settings in the system settings menu.

On vehicles with CODE 810 (Sound system), the audio equipment is not only equipped with the general tone settings (treble, bass and balance), but also with additional tone settings.

The function sequence for volume/tone settings is subdivided into the following subfunctions:

Function sequence for manual volume/sound settings 

The function sequence for manual volume/tone settings is subdivided into the following subfunctions:

The desired settings are relayed on vehicles with CODE 810 (Sound system) via MOST to the sound system amplifier control unit, where they are then processed. In vehicles except CODE 810 (Sound system), the settings selected are processed by the audio equipment. Audio output via the speaker system can be muted using the mute function button or using the corresponding button on the audio equipment.

Function sequence for volume settings via right multifunction steering wheel button group 

The volume for the audio and video sources is increased or decreased by pressing the + and - buttons, selecting specific functions and volume control. The control signals are forwarded by the steering wheel electronics via the following route:

Steering LIN →

Steering column tube module control unit →

Chassis CAN 1 →

Front SAM control unit with fuse and relay module →

Chassis CAN 2 →

Instrument cluster →

Interior CAN →

Audio unit

Function sequence for volume settings through the audio equipment 

Turning the "ON" button on the audio equipment increases or reduces the volume.

Function sequence for sound settings via audio/COMAND control panel 

The user can set the corresponding sound by selecting the "Sound" menu on the audio/COMAND control panel.

The Audio/COMAND control panel control signals are transmitted via the telematics CAN to the audio equipment.

Function sequence for speed-dependent volume control (SDV [GAL]) 

The volume is adapted to the noise level in the vehicle interior using the speed-dependent volume control, which is defined by the vehicle speed.

In order to make this adjustment, the instrument cluster sends vehicle speed information to the audio equipment via interior CAN. On vehicles with CODE 810 (Sound system), the audio equipment forwards information over MOST to the sound system amplifier control unit. In accordance with this information the audio equipment or the sound system amplifier control unit raises the output level or lowers it.

Function sequence for radio operation (FM, AM, HD radio) 

The antennas receive signals for the frequency bands FM (ultra-short wave) and AM (medium wave) and - not available in all national versions - short wave (SW)). The following useful signals relevant for the radio reception are modulated onto these signals:

FM-1 signals are received via the following route:

Windshield antenna →

FM, AM and CL [ZV] antenna amplifier →

Audio unit

FM-2 signals are received via the following path:

Windshield antenna →

FM 2, DAB and TV antenna amplifier →

Audio unit

The AM signals are received via the following route with the Vario roof closed:

Rear window antenna →

AM antenna amplifier →

Rear shelf antenna amplifier with selection switch →

FM, AM and CL [ZV] antenna amplifier →

Audio unit

The AM signals are received via the following route with the Vario roof open:

Rear shelf antenna →

Rear shelf antenna amplifier with selection switch →

FM, AM and CL [ZV] antenna amplifier →

Audio unit

The rear shelf antenna amplifier with selection switch reads in the status of the antenna switchover limit switch, and switches over in the event of a status change to the AM antenna amplifier or the rear shelf antenna.

The radio mode function sequence consists of the following subfunctions:

AM tuner function sequence 

For the MW and SW radio frequency bands, the useful signals are broadcast using amplitude modulation (AM). The AM tuner integrated into the audio equipment demodulates these signals. In other words, it separates the useful signals (audible frequencies) from the carrier signal (inaudible).

IMPORTANT SW signals are not received by all national versions.

Function sequence for FM double tuner with diversity reception (FM) 

For the FM radio frequency band, the useful signals are broadcast using frequency modulation (FM).

The dual FM tuner integrated into the audio equipment demodulates these signals. In other words, it separates the useful signals (audible frequencies) from the carrier signal (inaudible). The audio equipment integrates the signals from the FM, AM and CL [ZV] antenna amplifier and the FM 2, DAB and TV antenna amplifier to form an optimized signal (phase diversity).

IMPORTANT An additional tuner function is integrated in the audio equipment for additional information such as the weatherband or the FM multiplexer for the Vehicle Information and Communication System (VICS).

Function sequence for Radio Broadcast Data System (RBDS) (with CODE 494 (USA version)) or Radio Data System (RDS) (except CODE 494 (USA version), except CODE 498 (Japan version)) 

In addition to the radio program, many radio stations (FM) also broadcast additional digital information such as station name and traffic message channel recognition.

The additional digital information is evaluated by the audio equipment and shown on the Audio/COMAND display, provided that the following preconditions are complied with:

Function sequence, HD radio (with CODE 494 (USA version)) 

The audio tuner for HD radio integrated into the audio equipment decodes the digital signals. Additional information and services are shown on the Audio/COMAND display, e.g. Program Service Data, Artist Experience, traffic information.

Function sequence for digital radio (DAB) (with CODE 537 (Digital radio (DAB))) 

The tuner unit permits the reception of digital radio in DAB format. The stations are categorized into groups in DAB, so-called "Ensembles".

Control of the DAB functions is accomplished via the audio equipment. The information or displays required for control are shown on the Audio/COMAND display.

The DAB band-III signal (DAB 1) is received as follows:

Windshield antenna →

FM 2, DAB and TV antenna amplifier →

Tuner unit

The DAB 2 signal is received via the following route:

Windshield antenna →

TV 1 antenna amplifier →

Tuner unit

With DAB reception, the audio equipment sends the FM station lists over the MOST to the tuner unit. If a comparable FM station is found, this is then requested by the tuner unit and the audio equipment provides the FM audio signals on the MOST. If the DAB reception worsens, a switch is made to the audio equipment's FM station, whereby the tuner unit adjusts the time lag between the digital and the analog signal. In this way the switchover is almost inaudible ("Seamless Linking").

The tuner unit sends the audio signals via MOST to the audio equipment (except code 810 (Sound system)) or via the audio equipment to the sound system amplifier control unit (with code 810 (Sound system)).

DAB dual tuner 

The tuner unit is designed as a diversity tuner and provides the following advantages:

Function sequence for Satellite Digital Audio Radio Service (SDARS) (with code 536 (SIRIUS satellite radio)) 

The tuner unit makes it possible to receive stations from the "Sirius satellite radio" provider. The SDAR system is controlled through the audio equipment and the control occurs via MOST. The information or displays required for control are output via the Audio/COMAND display and also in the instrument cluster. Real-time traffic data (RTTD) is also transmitted via SDAR, which includes accident and traffic jam reports and traffic flow information. The data is made available to the navigation module of the audio equipment via MOST.

The Sirius satellite radio signal is broadcast 3 times to achieve a diversity of channels (using two satellites and one terrestrial transmitter). The multifunction antenna receives all three channels from the Sirius satellite radio (Sat 1, Sat 2, terrestrial station) and transmits these signals over a direct line to the tuner unit.

The tuner unit receives and decodes the signals and sends them via MOST to the audio equipment (except code 810 (Sound system)) or via the audio equipment to the sound system amplifier control unit (with code 810 (Sound system)).

Additional function requirements for DVD, CD audio 

Function sequence for DVD, CD audio 

The DVD/CD audio function enables audio CDs or audio DVDs (including MP3 and other formats) to be played.

User guidance for controlling DVD and CD functionality and displaying additional information is performed on the Audio/COMAND display.

The data exchange between the audio equipment and the Audio/COMAND display takes place via the telematics CAN, but the audio equipment transmits image and video data to the Audio/COMAND display via an LVDS line.

Additional function requirements for connections in stowage compartment (telephone compartment) beneath the front armrest 

Function sequence for connections in stowage compartment (telephone compartment) beneath the front armrest 

USB connector 1 and USB connector 2 are integrated into the multimedia connection unit. On vehicles except code 360 (HERMES UMTS), except code 522 (Audio 20 radio) and except code 367 (Live Traffic Information), external devices (e.g. USB memory stick (universal serial bus), iPods and MTP devices) can be connected via both USB connectors. On vehicles with code 360 (HERMES UMTS), code 522 (Audio 20 radio) and code 367 (Live Traffic Information), external devices can only be used via USB connector 2; USB connector 1 is marked with a battery symbol and can only be used to charge an external device.

In vehicles except code 360 (HERMES UMTS), except code 522 (Audio 20 radio) and except code 367 (Live Traffic Information), the multimedia connection unit sends the signals of the external devices directly to the audio equipment, and in vehicles with code 360 (HERMES UMTS), code 522 (Audio 20 radio) and code 367 (Live Traffic Information) this is done via the USB splitter.

IMPORTANT Model 172.4

as of model year 2017

with code 518 (Media interface)

3 adapter cables are enclosed to connect the external devices.

When connecting a device to the multimedia connection unit, the audio equipment switches over to the new media source. The audio equipment outputs the audio signals for the connected devices via the speaker system (except CODE 810 (Sound system)) or forwards them via MOST to the sound system amplifier control unit (with CODE 810 (Sound system)). User guidance is performed on the Audio/COMAND display. The audio equipment generates the display information and transmits it to the Audio/COMAND display via an LVDS line.

As well as the actual media files, metadata that is transmitted to the audio equipment is stored in the connected device. Metadata includes, for example, the title, interpreter, composer, album, genre, audio book, podcast, file identifier, file type (audio or video). This metadata can be displayed and searched by the audio equipment. This metadata is compiled by the audio equipment in a memory, the media database. It is then possible to search for the relevant metadata in the media database. The media database permanently saves the metadata of up to three devices. When one of these devices is reconnected, the metadata is updated. As soon as a fourth device is connected, the oldest metadata record is overwritten.

When playing pieces of music, the corresponding cover art is shown on the Audio/COMAND display if the cover art in question is stored in the portable terminal (e.g. iPod). The maximum file size for processing cover art is 5 MB. The audio equipment adapts the resolution to 240 x 240 pixels, 16 bit colors, and converts the file to the JPG format. When searching for albums or pieces of music on the connected device, the matching cover art is also shown on the Audio/COMAND display.

Additional function requirements for SD card (Secure Digital) 

Function sequence for SD card (Secure Digital) 

The SD card slot is integrated into the audio equipment. Audio data stored on an SD card can be shown on the Audio/COMAND display by activating the "Memory Card" media source and played back by the audio equipment.

Additional function requirements for storing audio CDs in the audio equipment (with code 494 (USA version) or with code 498 (Japan version)) 

Function sequence for storing audio CDs in the audio equipment (with code 494 (USA version) or with code 498 (Japan version)) 

Audio CDs can be stored on the integrated hard disk of the audio equipment and subsequently retrieved using the "Search" menu. The storage procedure is started during media operation by selecting "REC" in the "Media" menu bar. Only the entire audio CD can be stored on the hard disk. If the storage procedure is canceled prematurely (e.g. by selecting "Cancel"), no data is stored. Stored audio CDs can be retrieved using the "Search" menu in the "Media" menu bar. The individual tracks can also be retrieved using the general search function.

IMPORTANT Up to 12 audio CDs can be stored. When 12 audio CDs have been stored, an audio CD must be deleted before a new audio CD can be stored. In order to delete stored audio CDs, a stored audio CD must be played back. A stored audio CD can be selected for deletion using "Options" in the Media menu bar.

Additional function requirements for Bluetooth® Audio 

Function sequence for Bluetooth® audio 

The audio equipment can receive Bluetooth® audio signals from external devices via the Bluetooth® antenna and control the player of the external device. Bluetooth® audio is divided into the following subfunctions:

Search for devices and authorization 

The same options exist for the authorization of Bluetooth® audio sources as are available for telephony:

The device lists are set up the same for Bluetooth® audio and telephony. In the respective list, only those devices that support the corresponding Bluetooth® profile of the respective function are found or displayed during a search. With Bluetooth® audio these are Audio Video Remote Control Profiles (AVRCP) and Advanced Audio Distribution Profiles (A2DP), and for telephony it is the Hands-free Profile (HFP). If a device supports both functions, it appears in both lists after authorization.

Connection and reconnection 

An authorized device can be connected by means of selection in the corresponding list. If a device is connected that supports both HFP and AVRCP/A2DP, all profiles are connected. In this case the device is a telephone and the source of Bluetooth® audio at the same time.

On most devices, it is necessary to start the player on the device so that it can then be controlled via the audio equipment.

When starting, the audio equipment proceeds with the following strategy:

If a device is connected that only supports HFP and a change to the Bluetooth® audio application is made, "No Bluetooth® audio equipment connected" is shown on the audio equipment if corresponding audio sources are shown in the device list.

The "Connect last device" function bar enables the last used Bluetooth® audio source to be connected. However, the connection to the current telephone is interrupted here.

If a device is connected that only supports AVRCP/A2DP and a change to the telephone application is then made, the connection to the device is disconnected and the audio equipment begins the search for the last two telephones.

Metadata and display of information 

The display of information for Bluetooth® audio depends on the respective device used. If this device supports AVRCP 1.0, only "Audio streaming" is shown on the Audio/COMAND display and in the instrument cluster.

As of AVRCP 1.3, the track, album and artist are shown. In addition, the currently played time of the track can also be conveyed.

Furthermore, there is the option of changing between the normal track sequence and shuffle.

IMPORTANT It is possible to jump to the next or the previous track using the left multifunction steering wheel button group.

IMPORTANT Notes on supported devices for Bluetooth® audio can be found under: http://www.mercedes-benz.com/connect. 

  Electrical function schematic for Digital Audio Broadcasting function Model 172.4 as of model year 2017 with code 537 (Digital radio (DAB)) PE82.60-P-2057-97TAB
  Electrical function diagram for audio mode function   PE82.60-P-2058-97TAB
  Electrical function schematic for SDARS function Model 172.4 as of model year 2017 with code 536 (SIRIUS satellite radio) PE82.60-P-2066-97TAA
  Overview of system components, telematics   GF82.85-P-9999RD 
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