Repairing Window Switches on the Mercedes Benz M-Class
Yes, of course you know there will be a disclaimer. First of all, you must understand that I am in no way affiliated with Mercedes Benz. I am not an authorized mechanic for them or anyone else. I am simply a guy who likes to take things apart and put them back together, hopefully making them better (or at least not making them any worse) in the process.
The information contained on this page is strictly based on my own experiences and I am sharing this as-is with no warranties or guarantees. If you feel that you are not capable of performing these procedures, or if you are afraid that you may break something, or if you are very clumsy and often injure yourself when using tools, then please stop immediately and take your vehicle to an authorized mechanic!
It seems to be a common problem for the window switches on the Mercedes Benz M-Class vehicles to stop working. I have heard this reported by owners of model years 1998 through 2001. Hopefully, the 2002 model will not experience this problem, but only time will tell. The problem usually begins to manifest itself when raising a window. You will begin to notice that the window hesitates, or “stutters” as it is raised. The problem will eventually get worse, even to the point of being unable to raise the window. In some cases, applying extra force when lifting the window switch may allow the window to be raised, but eventually, that will also stop working.
The cause for this is in the design of the switch itself. As you will see in the following photos, the windows switches on the M-Class are a very good design except for one flaw: they rely on the spring action of copper alloy contacts. Because they are copper, they tend to bend slightly each time they are manipulated. Eventually, they will bend so much that they will be just out of reach for the plastic rocker that manipulates them. The repair method that I will describe is basically to bend the contacts back into position. This, of course, is only a temporary solution.
Step 1: Preparation
First of all, you will need some tools. You will need a long, medium sized Phillips screwdriver and a small flat head screwdriver. You might also want a low-speed, high-torque drill/driver with a Phillips bit. You should prepare a clean and well-lighted worktable for disassembling the switches. The first photo shows the M-Class center console in its undisturbed state. You will need to remove all items from the cubby in front of the gearshift and also from the cubby under the armrest.
Step 2: Remove the Console Wood Panel
Remove the rubber liner from the cubby in front of the gearshift by lifting on the front edge of it. There is no glue holding in place, just two rubber feet underneath. If you have the Mercedes Benz integrated cellular telephone, this cubby houses that connection and I am not sure if it must be removed or even how to remove it since I do not have this option.
Remove the gearshift knob by rotating its plastic retaining collar counter-clockwise until it clicks loose, then lift the knob from the metal shaft. Remove the black plastic trim that surrounds the gearshift selector plate by lifting straight up on it.
The felt cubby underneath the armrest is held in place by two Phillips head screws through the bottom of it. These screws may be very tight and difficult to remove, so take care not to strip the heads. A long screwdriver or an electric drill/driver will facilitate their removal. Once the screws are removed, the cubby will simply lift out.
You will now be able to reach through the cubby opening and push up on the underside of the console wood panel. It is held in place by standard trim clips, so It will take moderate pressure to release it. Lift the panel just enough so that you will be able to access the wiring harnesses beneath it.
Step 3: Remove the Wiring Harnesses
You will need to remove one connector from the cigarette lighter (it has no retaining clip). There are four multi-wire connectors and one single wire connector on the switch assembly. The white and blue connectors that are on either side of the switch assembly have retaining clips on the connectors themselves. The white connector that is on the rear has no retaining clip. The blue connector on the front has a retainer that is part of the switch assembly housing instead being part of the connector. The single pink wire has a very small retaining clip that is also part of the switch assembly.
Once all the wiring connectors have been released, carefully lift the panel over the gearshift and remove it from the vehicle. Take it to your worktable for the rest of the procedure. I would advise placing it on a towel or pad so that you do not scratch the wood panel (or plastic panel as is the case for pre-2000 model year vehicles).
Step 4: Remove and Open the Switch Assembly
The switch assembly is attached to the underside of the wood trim panel with four plastic clips: two on the front edge and two on the rear. Gently pry them with a screwdriver to release the switch assembly from the trim panel. Note that adjacent to the plastic clips are screw mounts, but there most likely will be no screws. My guess is that the plastic clips are used to make initial assembly more efficient, but that the screw mounts are there in case the clips are broken. In my case, I did in fact break two of the clips when trying to push and pull on the window switch when mine failed and this is part of the reason why I decided to attempt this repair myself instead of seeking warranty service.
Once you have removed the switch assembly, place the trim panel aside. In order to access the contacts, it is necessary to remove the cover from the switch assembly. The black switches that show through the trim panel are just plastic covers over the rockers that manipulate the contacts. These must be removed in order to remove the assembly cover. The covers for all the window switches, the central lock switch, and the rear defrost all need to be removed by prying on the sides at their pivot points. Also, you will need to remove the cover of the slide switch for the rear window lock. No part of the mirror control needs to be removed.
Once you have removed all the switch covers, you will now need to remove the white plastic rocker mechanisms for the central lock and the defrost switches. To do this, you will need to pry at the pivot points. Be very careful not to let the rockers jump out. They ride on a spring-loaded pin. You should not have a problem with losing these springs or pins as long as you keep the switch assembly flat on the worktable. Make sure you note the orientation of the rockers and which one belongs to which switch. Although they are the same part, they do ride on different contacts. With use, they can wear differently so putting them back in the same place can be important. The rockers for the window switches do not get removed at this time.
You can now open the switch assembly by prying at the eight indentions (two on each of the four sides). Once you have the cover open, set it aside. You will now be able to see the contacts inside. Again, take care to keep the switch assembly flat on the worktable to prevent any springs from falling out. If the springs do fall out, they are easily put back in place – as long as you don’t lose them!
Step 5: Adjust the Contacts
Although it could be any of the contacts that become problematic, it seems that most commonly it is the front window “up” control. To gain access to the contacts, you will need to remove the white plastic rocker for the switch. The window switch rockers are different from those used for the central lock and defrost switches, but they are still removed by prying at the pivot points. Again, be careful not the let the spring-loaded pin jump out from under the rocker.
With the rocker removed, you should now be able to understand what is happening when you operate the window switch. There are four possible positions for the front windows: stationary, down, auto down, and up. If you look at the bottom of the rocker, you will see three cams that manipulate the contacts as it is moved. The up position manipulates the right contact, down is the middle, and auto down is the left contact. You will probably notice that the contacts are not all aligned to the same height. This is because varying levels of force applied to them by the three cams causes them to bend into different positions (and this is the flaw).
To realign the contacts, use a small screwdriver to lift up under the very edge of the contact. This is the edge that angles down toward the circuit board. My suggestion is to gently bend it up and slightly back. This will make it ride more firmly against the cams on the rocker. The problem exists when the contacts become bent downward, away from the cams. I would recommend that you adjust all the contacts while you have the assembly open. Chances are if one window has been problematic, another is not far behind. Keep in mind that it is a good idea to note which rocker belongs to which switch since the wear patterns may be different. Also, make sure that the spring-loaded pins are properly aligned when you replace the rockers.
Step 6: Reassembly
Once you have adjusted the contacts, make sure you replace only the window switch rockers. You cannot replace the cover with the central lock and defrost rockers installed. When replacing the cover, make sure the rear window lock switch aligns with the hole in the cover. If not, it may push the cap (the part with the child symbol) off the cover and possibly break its retaining clips. If you are concerned about this, you could just remove this cap before replacing the cover.
Once you have the cover firmly snapped into the assembly, replace the central lock and defrost rockers and all the switch covers. Manipulate the switches to make sure everything is working smoothly and not binding. Also, this will let you know if you have lost a spring or if a spring did not properly align with a rocker.
At this point, I strongly recommend that you take the switch assembly back to the vehicle and temporarily connect it to the wiring to test all the functions. This will let you know if the repair has worked, and also identify any problems. I have had my switch assembly open three times now and the only problem I encountered was reversed rockers for the central lock and defrost which made the switches act a little finicky. A quick reversal and everything was fine.
Once you are satisfied that everything is working, you can now finish the project in one of two ways. You can unplug the switch assembly, take it back to the worktable and reattach it to the wood panel, thus exactly reversing the disassembly steps. However, at this point, it is possible to simply leave the switch assembly connected to the wiring and place the wood panel over it, snapping the two together. This is the most efficient method, unless your plastic clips are broken (like mine) and the switch assembly must be reattached to the wood panel with screws. If that is the case, then it will be best to do this reassembly back at your worktable.
Once you have the wood panel and the switch assembly reattached and the six wiring connections made (cigarette lighter, four multi-pin connectors and one single wire connector on the switch assembly), you are minutes away from completion. Simply snap the wood panel back into the console, reinstall the armrest cubby, replace the plastic trim around the gearshift indicator and the shift knob and finally the rubber liner for the front cubby.
You have just completed a task that not even the Mercedes Benz technicians have performed. Instead, they just replace the entire switch assembly, and (I assume) discard the old one. What wimps! Now that you have completed the project, enjoy your power windows. That is, until the contacts bend out of alignment again! Maybe someday, they will redesign the contact articulation so that this won’t be a problem any more. Until then, happy tinkering!
(You can click on the thumbnails below for larger images)