Hello again durinkos
I had a bit of time with the bike today. I put the rear suspension spring to the fully compressed position as you suggested, but this has not changed anything. I then tried the unofficial calibration with the GS-911 again, but the results are as before – same error messages. I’ve cleaned the connectors (again) and checked continuity from the ZFE to all of the connectors, front and rear – all OK. Powering the spring motor from an external 12V supply, I also checked the resistance at the potentiometer for different spring positions and this seems OK (resistance of between around 300 and 2200 ohms) so I’m satisfied that the spring preload adjustment works at the strut at least.
I don’t know how to measure or check the damper adjusters - they’re stepper motors I think.
With no official support for this early ESA in the GS-911, I think that I’ll have to take the bike to a BMW dealer for calibration with their diagnostic machine, though that won'y be for some time. If that fails, I may just abandon the ESA, either living with whatever damper settings I have and rigging up a switch under the seat for the rare occasions I need to adjust the preload, or buy non-ESA suspension units. The bike is old and does not justify the huge cost of even secondhand ESA parts.