I didn't catch the year model which makes a big difference. The later versions have self-diagnostics which can be interrogated and faults reset (if no fault currently exists).
Early units can only be tested with MB specific tools. In almost all cases if an airbag has deployed the crash profile sensor (control unit) will have to be replaced. This is for a very interesting reason.
Combined with the possible mechanical issues involved with the crash (or whatever event - saw a driveshaft coupling come apart at the rear of the tranny and set off the airbag as the crash profile sensor is above and forward on the tunnel), the crash profile sensor acts as a "Black Box" storing the pertinent issues of deployment; only to be recovered by factory means.
I was first made aware of this over ten years ago when our bodyshop foreman asked me if all airbag modules needed to be replaced when there was deployment. I dug into Bosch info I had at the time and found that: Yes, the module would have to be replaced and that the module retained info on the crash profile. The car in question, an early 300E, had the bag go off and both belt retractors exploded tight. The interesting thing was that the info said that the bag deployment threshold was modified by whether the seat belts were being worn. In this case it was obvious that the driver didn't have his seat belt on (the belt was pulled tight against the pillar) and the accident had been minor. We both wondered how badly the insurance industry would like to know this info which obviously was retained (but not easily accessible). It was very likely in this case that the SRS deployed because the threshold had been met for a driver without seatbelt, but could easily not have deployed had the belt been used.
The repair costs for the car were more than doubled by the necessary SRS parts. Who should pay here?? The insurance people had no idea and still don't, evidently as the next case shows.
This issue was even more openly addressed recently in the Jeroxxx Brxwx case. Highly paid football player who launched his Corvette into a tree at high speed killing at least himself. The issue was whether the airbag deployed causing the accident or as a result of the accident. GM brought out the "Black Box" data and blew the case out of court. The biggest issue that remained was that of privacy!!!
Bosch Master, ASE Master, L1
33 years MB technician