Did you every find out what it was... I am having the same issue with mine W210 E430 1998.. The SRS light stays on as well as the Air bag off light on the console.. Regardless if someone is sitting there or not..

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Peter L. House
1998 Sport E430
Azure Blue
110,000k Miles

1987 Oldsmobile Cutlass Salon
V8 Bucket Seats
Factory Moon Roof