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Home >> Mercedes Benz >> 2021 >> E450 Base, 2D Convertible >> Repair and Diagnosis >> Electrical >> Motors, Switches, Relays >> Electrical System - Body - 238 Chassis (2 Of 6) >> Basic Knowledge >> Audio Mode, Function >> Audio Mode, Function - GF82.85-P-2030FH

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

Model 238 

Up To Model Year 2019 

G15468151Courtesy of MERCEDES-BENZ USA

Shown On Model 238.3 With Code 531 (COMAND APS) 

G15468152Courtesy of MERCEDES-BENZ USA

Shown On Model 238.3 With Code 520 (Audio 20 USB) or With Code 522 (Audio 20 radio) 

G15468153Courtesy of MERCEDES-BENZ USA

Shown On Model 238.4 With Code 531 (COMAND APS) 

G15468154Courtesy of MERCEDES-BENZ USA

Shown On Model 238.4 With Code 520 (Audio 20 USB) or With Code 522 (Audio 20 radio) 

Function requirements, audio mode, general 

General information on the audio mode 

The head unit can be switched on and off using the "ON" button on the right lower control panel (with automatic transmission) or on the left lower control panel (with manual transmission) and the volume is set using the volume control button. On vehicles with code 246 (Analog clock), the menu for the radio reception or media sources can be called up via the upper control panel control unit.

The control signals from the left lower control panel, right lower control panel, or from the upper control panel control unit are received over the following path:

LCP LIN →

Audio/COMAND control panel →

Telematics CAN →

Head unit

The menu contents are generated by the head unit and shown on the Audio/COMAND display. The Audio/COMAND display receives the switch-on signal from the head unit via telematics CAN. The picture data is transferred by the head unit via a HSVL line to the Audio/COMAND display.

The audio mode functions can be selected, activated and set with the Audio/COMAND controller of the Audio/COMAND control panel. The "Back" button supports navigation in the menus. The control signal are transmitted to the head unit by the Audio/COMAND control panel via telematics CAN.

The functions of the audio mode can be operated with the touchpad (with code 448 (Touchpad)). The control signals are transmitted to the head unit by the touchpad via telematics CAN.

The audio mode functions can be selected, activated and set with the instrument cluster multifunction steering wheel button group and the head unit multifunction steering wheel button group. The volume can be adjusted using the volume control button on the instrument cluster multifunction steering wheel button group. An active audio source can be muted by pressing the mute function button in the instrument cluster multifunction steering wheel button group. The control signals are forwarded as follows:

Steering wheel electronics →

Steering LIN →

Steering column tube module control unit →

Chassis FlexRay →

Electronic ignition lock control unit →

User interface CAN →

Head unit

On vehicles with code 531 (COMAND APS), the audio mode functions can be operated with the voice control system. The voice commands are converted into electric signals by the driver hands-free system microphone and forwarded to the head unit.

IMPORTANT Radio stations and media sources can also be selected via the instrument cluster.

On vehicles except CODE 810 (Sound system) and except CODE 811 (Advanced sound system), the head unit outputs the audio signals corresponding to the volume and sound settings over the vehicle's speaker system.

In vehicles with CODE 810 (Sound system), the head unit forwards the audio signals and the volume and tone settings via the MOST to the sound system amplifier control unit, which actuates the speaker system.

In vehicles with code 811 (Advanced sound system), the head unit forwards the audio signals and the volume and tone settings via the MOST to the Advanced sound system amplifier control unit, which actuates the speaker system.

The audio mode consists of the following component functions:

Function sequence for volume and sound settings 

All volume and tone settings are selected using the head unit. This is done either by the user or automatically by the head unit. The sound settings are shown on the Audio/COMAND display. The sound settings can be changed individually for applications with the "Sound" menu and the system returned to the default settings via the system settings. On vehicles with code 810 (Sound system) or code 811 (Advanced sound system), the head unit has additional tone settings.

The volume and sound settings function is subdivided into the following subfunctions:

Function sequence for manual volume and sound settings 

Manually volume and tone settings can be selected as follows:

IMPORTANT The audio output via the speaker system is interrupted by actuating the mute function button in the multifunction steering wheel instrument cluster button group or by pressing the volume control button in the left lower control panel or right lower control panel.

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

The volume is adapted to the noise situation in the vehicle interior with the help of the speed-dependent volume control. The noise level in the vehicle interior is determined via the vehicle speed, whereby the assignment depends on the respective body variant. The instrument cluster transmits the vehicle speed data to the head unit via the user interface CAN. Corresponding to this information, the head unit, the sound system amplifier control unit (with code 810 (Sound system)) or the Advanced sound system amplifier control unit (with code 811 (Advanced sound system)) increases the output level or lowers it. The sound system amplifier control unit or Advanced sound system amplifier control unit receives the data for volume adjustment from the head unit via MOST.

On vehicles with code 810 (Sound system) or with code 811 (Advanced sound system), the SDV [GAL] is additionally optimized by interference recording with the driver hands-free system microphone and the front passenger hands-free system microphone. The sound system amplifier control unit or Advanced sound system amplifier control unit receives the signals of the driver and front passenger hands-free system microphone from the head unit via MOST and adapts the volume of the audio output.

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

The antennas receive signals for the FM (ultra-short wave) and AM (medium wave) frequency bands. The following useful signals relevant for the radio reception are modulated onto these signals:

Vehicles with code 494 (USA version) are equipped for reception of HD radio. In HD radio, digital signals are sent over the radio frequencies along with the analog signals. This makes audio signals available in better reception quality, and additional information and services can also be received and used. These signals are processed by the audio tuner integrated in the head unit.

The FM-1 and FM-2 signals or the HD radio signals are received via the following route:

Rear window antenna (model 238.3) or windshield antenna (model 238.4) →

FM, AM, CL [ZV], DAB and KEYLESS-GO antenna amplifier (FM 1) and FM 2, DAB and TV antenna amplifier (FM 2) →

Head unit

The AM signals on model 238.3 are received via the following route:

Rear window antenna →

FM, AM, CL [ZV], DAB and KEYLESS-GO antenna amplifier →

Head unit

The AM signals on model 238.4 are received via the following route when the soft top is closed:

Soft top AM antenna →

AM amplifier →

AM amplifier with selection switch →

FM, AM, CL [ZV], DAB and KEYLESS-GO antenna amplifier →

Head unit

The AM signals on model 238.4 are received via the following route when the soft top is open:

Left rear side paneling antenna →

AM amplifier with selection switch →

FM, AM, CL [ZV], DAB and KEYLESS-GO antenna amplifier →

Head unit

The AM 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 soft top antenna with AM amplifier or the left rear side trim antenna.

The radio mode function sequence consists of the following procedures:

AM tuner function sequence 

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

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

IMPORTANT Model 238

up to model year 2019

with code 498 (Japanese version)

An additional tuner function is integrated in the head unit for the VICS-FM multiplexer (Vehicle Information and Communication System) additional information.

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, type of program and traffic message channel recognition. This information is evaluated by the head unit and shown on the Audio/COMAND display, if an RDS or RBDS station is tuned and the "RDS" or "RBDS" function is activated.

Function sequence for HD radio, With Code 494 (USA version) 

The audio tuner integrated in the head unit decodes the digital signals. Additional information and services are shown on the Audio/COMAND display, e.g. program service data, artist experience, traffic information.

Additional function requirements for Secure Digital (SD) card (With Code 355 (Preinstallation for navigation retrofit), With Code 357 (Map navigation) or With Code 531 (COMAND APS)) 

Function sequence for Secure Digital (SD) card (With Code 355 (Preinstallation for navigation retrofit), With Code 357 (Map navigation) or With Code 531 (COMAND APS)) 

Audio files stored on an SD card can be shown as a media source by the head unit on the Audio/COMAND Display and be played back. The SD card slot with card reader is integrated in the multimedia connection unit. The head unit reads in the signals of the multimedia connection unit.

Additional function requirements for media connections 

Function sequence for media connections 

USB port 1 and USB port 2 of the multimedia connection unit and the front center console USB port (with code 896 (Vehicle access and drive authorization via mobile phone), code 897 (Wireless mobile phone charging) or code 899 (Multifunction telephony)) can be used to connect external devices (e.g. USB (Universal Serial Bus) flash drives, iPods, MTP devices). The multimedia connection unit and the front center console USB port are connected to the head unit through direct lines.

IMPORTANT Model 238

up to model year 2019

with code 518 (Media interface)

3 adapter cables are enclosed to connect the external devices.

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 head unit adapts the resolution and converts the file into JPG format. When searching for albums or pieces of music on the connected device, the corresponding cover art is also shown on the Audio/COMAND display.

Function sequence for digital radio (DAB) (With Code 537 (Digital radio (DAB))) 

The head unit (with code 531 (COMAND APS)) or the tuner unit (with code 522 (Audio 20 radio)) enables the reception of digital radio in DAB format. To ensure reception diversity (selection of the best signal), the head unit or tuner unit receives two DAB band III signals (DAB 1 and DAB 2). With DAB, the stations are categorized into groups known as "Ensembles". User guidance takes place via the head unit. On vehicles with code 522 (Audio 20 radio), the head unit and tuner unit communicate via MOST. The information or displays required for operation are output by the head unit via the HSVL line on the Audio/COMAND display.

With code 531 (COMAND APS), the DAB 1 signal is received via the following route:

Rear window antenna (model 238.3) or windshield antenna (model 238.4) →

FM, AM, CL [ZV], DAB and KEYLESS-GO antenna amplifier →

Head unit

With code 531 (COMAND APS), the DAB 2 signal is received via the following route:

Rear window antenna (model 238.3) or windshield antenna (model 238.4) →

FM 2, DAB and TV antenna amplifier →

Head unit

With code 522 (Audio 20 radio), the DAB 1 signal is received via the following route:

Rear window antenna (model 238.3) or windshield antenna (model 238.4) →

TV 1 antenna amplifier →

Tuner unit

With code 522 (Audio 20 radio), the DAB 2 signal is received via the following route:

Rear window antenna (model 238.3) or windshield antenna (model 238.4) →

FM 2, DAB and TV antenna amplifier →

Tuner unit

The FM double tuner provides the FM audio signals when the DAB mode is active. If the DAB reception starts to deteriorate, reception switches over to the FM station, but only after checking and ensuring a better signal reception. In the process, the head unit (with code 531 (COMAND APS)) or the tuner unit (with code 522 (Audio 20 radio)) compensates for the time offset between the digital and analog signal.

This makes the switchover almost inaudible ("seamless linking").

The DAB 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 (with code 522 (Audio 20 radio)) or head unit (with code 531 (COMAND APS)) enables the reception of stations from provider "Sirius Satellite Radio". The SDARS system is controlled via the head unit and is implemented using the MOST with code 522 (Audio 20 radio). The information or displays required for control are shown on the Audio/COMAND display.

To achieve a diversity of channels, the Sirius satellite radio signal is broadcast 3 times (using two satellites and one terrestrial transmitter). All three channels of the SIRIUS satellite radio (Sat 1, Sat 2, terrestrial station) are received by the SDARS antenna.

The SDARS antenna sends the signals via a direct line either to the tuner unit (with code 522 (Audio 20 radio)) or to the head unit (with code 531 (COMAND APS)), which receives and decodes the signals. With installation of the tuner unit, the signals are sent to the head unit via MOST.

Additional function requirements for Bluetooth® Audio 

Function sequence for Bluetooth®audio 

The Bluetooth® antenna allows the head unit to receive Bluetooth® audio signals from external devices. Bluetooth® audio is divided into the following additional information:

Search for devices and authorization 

The same options exist for the authorization of a Bluetooth® audio source 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 head unit.

When starting, the head unit proceeds with the following strategy:

On vehicles with code 899 (Multifunction telephony), the head unit searches for the two mobile phones that were last signed on, first via near field communication and then via Bluetooth®. The first mobile phone to respond to the request is connected.

In vehicles with code 379 (Telephone module with Bluetooth® (SAP)), the head unit first searches for the last two SAP telephones (SIM Access Profile) used in the vehicle. The first SAP telephone that replies to the query is connected if it is not connected to any other device via Bluetooth®.

If no mobile phone is found via the near field communication or Bluetooth® communication and no connectible SAP phone is found, the head unit searches for the last two mobile phones used in the vehicle. If one of these devices is found, the head unit connects to this device. If this device also supports AVRCP/A2DP, these profiles are also connected.

If a device is connected that only supports HFP and it is changed to the Bluetooth® audio application, "No Bluetooth® audio equipment connected" is shown on the head unit if the corresponding audio sources are shown in the device list. The "Connect last device" menu 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 head unit 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.

IMPORTANT "Audio streaming" is also indicated 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 head unit finger navigation pad (S163/2s10).

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 238 up to model year 2019 with code 522 (Audio 20 radio) with code 537 (Digital radio (DAB)) PE82.60-P-2057-97DCA
  Electrical function diagram for audio mode function   PE82.60-P-2058-97DCA
  Electrical function schematic for SDARS function Model 238 up to model year 2019 with code 522 (Audio 20 radio) with code 536 (SIRIUS satellite radio) PE82.60-P-2066-97DCA
  Overview of system components, telematics   GF82.85-P-9999FH 
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