Since this thread is discussing the one-time tensioned seat belts during a low impact, I though I would pass along a repair option of air bags and seat belts. This will be a lower cost option than buying new from MB. I'm not affliated with them. Check them out here: MyAirBags.com
Mystery Solved! The SRS warning light and the smell of gunpowder were due to the seat belt pretensioners having deployed upon impact. Seat belt pretensioners are pyrotechnic, just like airbags, which explains your gunpowder smell. It also explains the SRS warning message, since the pretensioners are part of the Supplemental Restraint System.
Most people wouldn't think to check the rear seat belts, especially if the rear seat had been unoccupied during the crash. However, on certain Mercedes models (211, 212, etc.), the rear belt tensioners will fire, even if the rear seat belts are not in use.
(The owners manual uses the term Emergency Tensioning Devices (ETDs), to differentiate the one-time, pyrotechnic tensioning function from the electric, reversible tensioning function of the PRE-SAFE system.)
Hope this solves the same mystery for anyone else who gets rear ended and wonders why the SRS Warning Message appears, even though no airbags deployed.
Incidentally, I had a similar head-scratching experience years ago with my W220, after we were involved in a minor frontal collision. No front airbags deployed in the W220, yet the SRS Warning Message was on afterwards. Turns out the driver seat belt pretensioner had indeed fired. Upon further research, I confirmed that the vehicle's sensors determine crash severity in real time during the collision and therefore can deploy the elements of the Supplemental Restraint System in sequence, not all at once. Our frontal collision generated only enough deceleration force to trigger the belt tensioner to fire, but was not severe enough to also require the front airbag(s).
The Germans are always thinking...
I’m surprised the rear self belt tensioners even went off when no one was sitting in the back seat (I was the only person in the car at the time of the accident) and obviously they weren’t buckled in. After the interior detail the body shop did, there is no trace of any gunpowder smell and the car smells like it did the day I bought it. Lol. And you’re right. I didn’t even think to check the seatbelts, I thought it was the deployed headrests causing that smell.
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
