Many of you are aware that the volume knob on the W204 C-class, and other models, can be frustrating specifically during colder months. The sensitivity of the knob will seemingly disappear and will no longer accurately change the volume level. Once the cabin warms up the knob may begin to work properly again but usually this is not guaranteed. Basically the volume knob is junk and Mercedes-Benz should've done a better job with such a commonly used component.

This write-up aims to show you how to perform a semi-permanent fix by cleaning out the dial underneath the knob with contact cleaner. The dial used for volume control is what is called a rotary encoder. It is similar to a potentiometer except you can turn it infinitely, whereas a potentiometer has two stop points. Both function similarly in that there are brass wipers inside that slide across a contact plate. Overtime dust gets inside creating grime that causes the dial to either work sporadically or not work at all. Cleaning out the dial solves these problems.

For more information on how a rotary encoder works, watch this video: https://youtu.be/v4BbSzJ-hz4

For the contact cleaner, use something like this: https://www.crcindustries.com/produc...-oz-02130.html




Step 1: Remove the head unit by following these instructions: https://www.pelicanparts.com/techart...eo_Removal.htm




Step 2: Remove the lower switch bank by removing the four T15 screws securing it to the head unit.












Step 3: Remove the face plate from the head unit by removing the four PH2 screws holding it on.










Step 4: Remove the volume knob by simply pulling on it.








Step 5: Remove the circuit board from the face plate by removing the nine PH1 screws holding it on.






Step 6: Spray contact cleaner liberally into the dial in between the outer plastic drum and metal bracket. Occasionally spin the dial back and forth and completely around then spray again. Do this multiple times. Do this outside or over a towel to catch run off. Do this in a well ventilated area. The idea is to dissolve the grime and wash it OUT of the dial so do not be stingy with the contact cleaner.






NOTE: Opening the actual dial is tricky and not recommended. The metal bracket is pressed around the switch holding it together. But first the dial has to be desoldered from the circuit board. There are two points where the bracket is soldered and three points where the electrical leads of the dial are soldered. Once these are undone the switch will come off. The bracket will have to be pried away from the dial before the dial can be opened. This will most likely destroy the dial or make it difficult to put back together. Since this is a custom made component a replacement will not be easy, if not impossible, to come by.










Step 7: Reassemble everything in the reverse order. If you had something in the PCMCIA make sure to remove before putting the face plate back on. Otherwise you may nearly break the door off.






My immediate results seem to be promising and the volume knob seems to respond much better than it had before. But time will tell how long this solution lasts.

 

After about 2 weeks I can say this has markedly improved the function of the volume knob. I thought that shortly after cleaning the knob would go back to behaving poorly but it's still working fine. It has an instantaneous response now rather than needing to slowly rotate it to increase volume.

 

I cannot take your instruction seriously.

Your radio unit shows no skin peeling at all.

 

Any idea if that faceplate can be replaced from a donor unit? Or will it trigger anti-theft protections?

 

I don't think it will. The faceplate is just buttons with an input board. The board is easily swappable.

 

I have a ‘14 cls550 and my knob is stuck, it does not rotate anymore. It worked fine yesterday. Can I simply pull on the knob to get it out and clean it?

 

The knob should be a similar design so it's probably removed by simply pulling on it. I have no idea what would've caused it to seize though. Hopefully you can figure it out.

 

Hey man, I just want to say thank you. Your instructions and write up are nice and clear. It restored my volume knob function back to 100 %. Thanks again.

 

Awesome, I'm glad this helped you!