They may have simply stopped working. Mine quit last year. Both sides at the same time. The fuse is okay. Once in a great while I'll open the car door to find the seat belt presenter in the extended position.

I don't know what the fix is. To some extent I say good riddance, since one thing I hate about Mercedes vehicles is the complexity of "convenience" features.

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95 E320 Cabriolet, 169K