If you are experiencing a B009612 or B009615 fault with a message along the lines of: “The crash sensor has a malfunction. There is a short to positive or an open circuit” and replacing the sensor in the door has not solved your issue there is a good chance the door hinge wiring loom is damaged.
WARNING: Before working on any part of the airbag system it is advised that you disconnect your battery.
Since the early 2000s most manufacturers have been using an environmentally friendly thermoplastic on wiring looms, in the early days there were very brittle but over time these materials have improved however they are still not as forgiving as the plastics that were used in the past which means sections of loom that experience lots of stress can fail causing all sorts of random and hard to diagnose electrical gremlins.
(For some perspective the car in the photo is a 2017 GLC with only 60k miles on the clock.)
The connector on the door of this generation Mercedes is has a slide on the bottom to release it which needs to be pulled out with equal force on either side (which can be tricky).
Once the connector is removed you will be able to pull back the rubber weather protection and inspect the loom:
The crash sensor is a very thin brown wire with a white line (although inside the door it is a brown wire with a green line) if you can spot a break you have found your problem!
Repairing can be quite fiddly but it is possible: you need to carefully expose the conductor on either broken wire, slip a piece of suitable heat shrink over the longest side and then carefully solder in a small length of similar gauge copper wire after which you can slide the heat shrink over it and heat.