On that model the diags socket should have the following pins connected
Pin 01 - Brown/Black - Diags pin to Motronic
Pin 02 - Brown/Blue - Diags to ABS (only if fitted)
Pin 04 - Brown - Earth
Pin 06 - Red/Yellow - Unswitched Power (also known as KL30 or Bat+)
Pin 09 - Blue - Rectifier
Pin 10 - Yellow/Gray - Switched Power (also known as KL15 or Ign On)
For basic comms checks, it is pins 1, 4, 6 and 10 which are relevant and the GS911 is suggesting no power on pin 10
Check for voltage between pin 4 and pin 6 with ignition off to confirm that is in place
Check for voltage between pin 4 and pin 10 with ignition on to confirm that is in place
Plus check continuity of pin 1 back to the Motronic
Ah I am also old school but much prefer processor based systems, but I have worked with electronics and processors all my life