I don't suppose this is your scenario? Excerpt taken from :
https://www.newtis.info/tisv2/a/en/e...-right/XTMlhsE
Would help if you identified your vehicle, though LCM function is probably universal across the years / engine options.
Functions, general
Diagnosis as well as communication with other control units takes place via the I-bus (E38/E39 high) or K-bus (E39 basic).
In the event of the control unit or one of its peripheral elements failing, an emergency operation facility maintains following functions.
- The outer rear lights (no licence plate light) low beam light, are switched on at "terminal 15 ON" irrespective of the position of the light switch.
- The left and right brake lights are switched on at "terminal 15 ON" and the brake light switch operated.
No communication via the I-bus/K-bus, i.e. also no diagnosis, is possible in emergency mode.
If a trailer coupling is installed in the vehicle, the lamp circuits of the pulling vehicle with a trailer module must be disconnected from those of the trailer. The LCM is connected to the trailer module via a data link.
A diagnosis program is provided for all 3 function spheres of the LCM.