has anyone replaced this part. had srs light checked at dealer and he identified this as the culprit. does the seat cover have to be removed? and is it difficult. also , can the switch just be fixed?

Did they mention this was the child seat recognition sensor? It's part of what they called the "baby smart" system that recognized when you had a MB child seat installed and would shut off the passengers side airbag. Otherwise I'm not familiar with a general-type occupancy sensor on that car. If it's the child seat one, in addition to the warning light for SRS, usually the small light down on the console is also lit, I think the light says "passengers side airbag off" or something like that.
Gilly

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Yes, the seat cover must be removed. If you're comfortable doing upholstery work it's actually a pretty simple job. Also, there isn't actually a switch. The Automatic Child Seat Recognition (ACSR) sensor uses antennae and evaluation electronics to read the transponder, located in approved MB infant/child seats. It uses pressure sensors to determine if the seat is occupied or not. Why don't you go to your dealer's parts department and take a look at one? You'll probably know right away whether or not you want to try it yourself. If you decide to give it shot, buy a couple of the white plastic clips that hold the seating surface to the frame. A few of them almost always break during dis-assembly. Good luck

Mike (I think it's Mike? "ILUVMILS"); It's not a pressure sensor at all, just an antenna and the box underneath the cushion, which senses the Babysmart seat. The Babysmart has a transponder built into it, and that's what the antenna is looking for. The box is just to convert it into a signal and sent to the SRS control module. They still marketing those seats? Thought they had a few probs and chickened out on the whole thing.........ACSR still around in the new cars? I couldn't remember the acronym for it, forget the "A", automatic.
Gilly

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Sorry to disagree Gilly, but there are sixteen membrane pressure sensors built into the unit. There are two separate antennae, one for transmitting, the other for receiving. The "box", is the evaluation electronics I referred to in my previous post.
Like everything else, ACSR has evolved. The latest system is known as WSS (Weight Sensing System). It uses four separate sensors, mounted on the front passengers' seat frame, as well as a dedicated control module. It's used to classify the size of the occupant into one of five categories.

1. Seat not occupied.
2. Typical weight of a one year old child, including child seat. (ANY CHILD SEAT)
3. Child or small adult.
4. Average size adult.
5. Large adult.

The idea is to pre-determine the threshold level of airbag deployment, depending on the severity of the accident.

I think there is a recent DTB on that code. It says the code could be caused by an electronic device (i.e. lap top, phone or blackberry) placed on the seat. What is the exact code number and model of car?

I looked at the DTB today - looks like it covers every model with babysmart. It says the code could be caused by anything with a memory chip (office id cards, phones laptops etc.) I would erase the code and be careful what I put on the front seat and see if it comes back.

many discussions in this thread, you can get the problem settled by a 30-buck seat sensor emulator

srs passeneger seat sensor ? - Mercedes-Benz Forum