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Created: 30 Apr 2008

Last Updated: 3 May 2009

Version 1.2 2nd May 2008

This short document describes the audio systems in the W211 E class and W219 CLS Class up until mid 2008 (i.e until the end of MY2008 production) for Europe, Middle-East, Africa. Asiapac. Australia & NZ vehicles. US/Canadian vehicles are subtly different, Japanese vehicles very different.

I yet to write up installation instructions for the upgrades mentioned below, so this is s document describing what can be done and not how to do it.


The E/CLS class (and in fact all Mercedes since about mid 2004) have a fibre optic bus connecting the audio components in the car together called MOST bus.

At a minumum there is the Audio Head unit (i.e the one with the buttons/display) and the Audio Gateway (AGW)

The AGW contains the amplifer, radio tuner(s), fibre optic controller, and diagnostic interface.

Some of the Head units have the AGW built into the same box, some have a seperate AGW located somewhere else in the vehicle.

Other Audio components found on the MOST bus include the Phone system, Voice Recognition, CD Changer and TV tuner.

Types of AGW:

If the car has a navigation system which is to have the TMC feature which redirects you around traffic congestion, the AGW needs to have 2 tuners, so that one can tune into the radio station transmitting TMC information. In the UK that is Classic FM

The AGW contains the amplifier, so there are different AGWs for cars with Harmon Kardon sounds system and those without.

On head units with AGW built in, the speaker wires for the car appear at the head unit, on cars with seperate AGW the speaker wires are routed to t he AGW in the boot (trunk), which is on the left hand side of the boot, tucked up between the inner and outer wings.

The dual tuner AGW has 2 aerial inputs, one is black and one is mustard colour - they are FAKRA type connectors. Some single tuner versions have a mustard blank instead of a connector, so be careful to find the right ones.

Here is a picture of a dual tuner, standard AGW.

Mercedes AGW picture

Audio Systems found in the W211/W219 E/CLS.

There are a number of different Audio Systems that have been factory fitted:

  1. Audio-20-Cassette. This system was fitted to the early W211 E Classes. It has a single tuner AGW in the boot (trunk) and the head unit. It does not have an AUX input
  2. Audio-20-CD:  This is the default fitment to current E/CLS Class cars and has the AGW built in to the head unit's case. It does not have an AUX input.
  3. Audio-50-APS is a Black and White Navigation unit that has a seperate AGW in the boot, but the map disk is in the head unit. It does not have an AUX unit.
  4. COMAND APS has the display up front, the AGW in the boot, and the Navigation unit in the boot.  COMAND APS head unit can be used without ever having a Navigation unit, but it needs  the AGW - obviously you'll get no Navigation, and in some markets cars are delivered like this. COMAND APS has an AUX input. COMAND APS can play DVD and MP3 disks in the DVD slot it has (subject to it having been upgraded to the latest software in it).

Note that there are two different types of COMAND unit - one with Video input (for TV) and output (for  rear screen), and one with no video inputs/outputs. Early models always had the Video sections, now by default cars do not have it unless you order TV or rear video screen.


iPod kits:  The Mercedes iPod kit needs an Aux input on the head unit so it can deliver the sound - only the COMAND-APS head unit has this.

Head Units:

  1. Audio-50-APS:    You can replace the head unit with COMAND APS head unit. Assuming you still want navigation then if your tuner is only a single tuner AGW you will have to replace that and you will also need to install the Navigation processor and various cables & brackets. If your left hand boot liner has no hole in it to access the navigation unit then you will need to replace that also.
  2. Audio-20-Cassette:  I believe that you can just switch the head unit to the COMAND APS unit to get a nicer sounding more functional head unit. If you want to add the Navigation facilities it is the same as mentioned for the Audio-50-APS
  3. Audio-20-CD: This is the difficult one because you need to replace the speaker wiring / power loom for the head unit with a new one, which at least means running fibre and wiring looms up and down the car. You will also need to install an AGW (and need the AGW mounting bracket) and the Navigation processor etc mentioned for the Audio-50-APS.  There is an AGW 'retrofit' loom which makes life slightly easier then the original factory fit loom - but I have not found a good source of these. Sometimes they appear on eBay (see purchasing section below).

Note, if you are installing COMAND APS with Navigation processor, then you should consider installing the iPod kit at the same time, as it needs cable run from front to back of car as-well and its easy whilst the boot trim and head units are out.

If you are replacing a single tuner AGW with a dual tuner AGW you will need an antenna splitter cable - I have yet to find the part number for this.

Note: If you install a new head unit and it  turns off a few seconds after displaying the Mercedes Star, it means that the unit needs it's fibre optic bus settings configured by the Mercedes dealer with Star Diagnosis workshop system.

After upgrading the head unit your CD changer, phone system and voice recognition (if you have those options) should continue to work fine, although it may be necessary to flash upgrade the phone system (or in worst case replace the phone controller) on very early cars.


You can purchase new dual tuner AGWs here.

Use my Ebay Search Tool to find parts on eBay - it searches in muliple languages and for common mispellings so is more likely to find what you want.

If you found this information useful, please support the site by making a donation via Paypal. Any amount at all helps me improve the information on the site.

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