Siemens SINUMERIK 828D Function Manual page 295

Internally simulated drives are used for all axes which had settings on the removed drive numbers. If the
controller is engaged for the drives that are still installed, these drives operate in the normal way. Interpolative
traversal of all axes is disabled.
Note
If alarm 300003 "Axis xx drive yy incorrect module type zz" appears, then you have removed
only one part of a 2­axis module. In this case, you should check the module type in the drive
configuration display. "NO" axis type is shown for removed modules.
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
D1: Diagnostics tools
5.6 Identifying defective drive modules
295