It is most likely a bad Signal Acquisition Module (SAM), which functions similarly to a network router, taking signals from the button, comparing them to warning and safety system inputs, and then activating the system you have chosen or else giving you a warning indication of a malfunction. Cost of a new one is approximately $800; labor could run more. Failure of one SAM could indicate possible problems with the other two - not always, but it is a possibility. Check all of them, especially the one under the rear passenger side seat, which can give problems with things like the soft close feature, brake lights, starting, and so forth. A common cause of SAM failure is water entering the car through a plugged drain in the main air intake for the heating and air conditioning system, just ahead of the front passenger side windshield. Another is being careless with a high pressure hose while washing the engine compartment (the SAMs in the engine compartment are under and attached to each large fuse panel; the one in back is attached to a fuse panel located behind the bezel for the right side passenger footwell courtesy light). SAMs do not like water.

Be sure that whoever does your prepurchase inspection 1) does not work for the seller, and 2) is a certified MB technician, whether dealer or independent.

If you get this car (or another W220), check out the W220 S-Class Encyclopedia sticky toward the top of the W220 forum page. You're new enough and likely under some time constraints, so I'll give you the link - http://www.benzworld.org/forums/w220-s-class/1508080-w220-s-class-encyclopedia-start-here.html Don't let it scare you. No one has all the problems described. It is a compendium of the best writeups on a wide range of problems experienced by (literally) thousands of owners, with solutions and tips that can save you money. There is an advice section on purchasing pre-owned W220s as well.

 

Thanks for the info. I have also read where simply swapping out the dash button module can do the trick sometimes. I hope it is something closer to that than a SAM problem.


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It could be; I have seen one other writeup where that was the cause, but only one. In the rest, it has been the SAM. Please let us know how it works out.

 

So the seller took the car to a mechanic to have the dash buttons look at. It is actually the independent Mercedes mechanic that I use for my wife's Mercedes. Long story short, the mechanic says he fixed the dash buttons by reconnecting a wire that had been disconnected in the fuse box. It's great that he got them working, but that seems very unusual. Why would a wire have come disconnected in the fuse box? I like the car and it drives well but that still makes me a little nervous. Any thoughts?

 

Hi sorry to bring up a old post but which fuse box had the lose wire

 

Can't begin to answer why the wire was disconnected, but glad it was something simple. The wires don't just "fall out" in these cars - someone disconnected it. As long as it works, don't worry. Enjoy the car.