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Have you verified the status of the Airbag Electronic Control Unit (ECU) fuse? The airbag should activate simultaneously with the radio, kombi, A/C, and other systems. The device receives a continuous power source from the battery, as well as a power supply that may be turned on and off (KL.R).
Additionally, are you capable of establishing communication with any additional K-Bus Electronic Control Units (ECUs)? (For example, HiFi, Radio, Sunroof, EWS, MFL, PDC?) If not, the problem is inside the BC1 and the other components of the vehicle. In the event of a short or open circuit in the K-Bus, it is anticipated that an error code would be recorded in the BC1.

Have you tried using a generic Bluetooth OBD connection for the DME? There are two methods of communication with the DME. The first is a direct approach via OBD messages, specifically with generic code readers. The second method involves using a laptop, Ediabas, and INPA to connect with the DME through the Kombi.

Greetings!
1. Affirmative, I have verified the MRS fuse and it is functioning properly. 2. The airbag unit is likely operational in terms of power, but it cannot be detected via communication channels, similar to the EWS and DME systems. It is worth noting that my vehicle does not have a sunroof, PDC, or a factory-installed radio. Consequently, the multifunction steering wheel (MFSW) only controls the cruise control and horn, rendering the remaining buttons non-functional.
3. The DME may be accessed using a more sophisticated OBD device, which reveals the presence of an internal defect. However, the specific details of the fault cannot be determined, and it cannot be cleared. The operation of the engine management system is satisfactory, as the vehicle runs and drives smoothly without any troubles. There are no check engine lights or instances of the car going into limp mode. I will attempt it in ISTA, maybe.

Thank you.

When you connect to the OBD port. It immediately establishes a connection with the KOMBI for K-Bus ECUS. The Kombi serves as the interface that links to the BC1. The BC1 then establishes communication with all other K-Bus ECUs present in the car. The K-BUS star point for the vehicle is located on the right side of the car, under the lower sill trim.

I recommend inspecting the K-Bus pinning on the BC1 for signs of corrosion. The pin 53 on the white connector and the connection between BC1 and Kombi. The KOMBI is not linked to the previously stated star point. The BC1 is directly connected to it. The Blue BCM connection has two pins, 28 and 46, which are both connected to the K-Bus in the dashboard harness. I am unsure which one of these pins is directly connected without referring to my notes.

Excellent information! Thank you much! Currently, I am anticipating the arrival of a pre-owned cluster. It is possible that the gateway has malfunctioned.