So I did same thing. Removed $540 and coded $544 to DSC, KOMBI, JBBF (as I thought it is necessary to copy messages from PT-CAN to D-CAN)...
First of all, I am surprise my +/-5mph stalks don't work. Is there any other cruise control option? Or maybe SZL didn't really got coded with DSC.
Maybe I will try to change that SZL_Codierdaten to E9x..
Before I coded it, I had reverse engineered some of the can messages. Message 0x200 (duplicated on PT-CAN and K-CAN) was used to pass information of cruise control speed set point. This was read for sure used by Kombi for the display. I know, because I injected some speed values on the CAN and they appeared on the display.
After the 544 coding, this can message id disappeared from PT-CAN and K-CAN (powertrain and body). You can observe he messages
here - just search for Cruise...
Now the communication must happen in different way, but for some reason KOMBI doesn't know the new way. I will try to find out whether there is different CAN message id used now for the speed set point communication.
Also, I wonder who is master and slave there. I thought it was DME figuring out the speed target and controlling to it (and just reporting target on PT-CAN which then would be translated by JBBF to K-CAN). But know, after seeing DSC coding options, like acceleration values for braking and acceleration, it makes me think that with 544 option it is DSC requesting engine torque and controlling brake.
System overview.pdf
So in option 540, I am pretty sure communication was as follow:
SZL stalks -> F-CAN cruise request -> DSC copy to PT-CAN -> PT-CAN cruise request -> DME speed control -> PT-CAN speed target reporting -> JBE copy to K-CAN -> KOMBI display
Now, in 544 I think DSC controls speed by sending torque request over PT-CAN to the engine. It should send also the speed setpoint for the display.
I will find out.
Do you guys use the latest KOMBI firmware? I have KMBI_PL2.C08 according to nscexpert, but apparently there is also C09.