Siemens alarm 400201: PLC STOP due to DB loading in the RUN state: DB%Z
SINUMERIK PLC system alarm · Siemens 840D/810D powerline
What it means
An existing data block (%Z identifies it) was reloaded into the PLC while the CPU was already in RUN. Because the running cyclic program may be using that DB at the moment it changes size or content, the system forces the PLC to STOP to protect process consistency. A full restart is required before the machine will leave this state.
Likely causes
- STEP 7 download of individual DBs performed online during RUN instead of after STOP/restart
- Basic or user program update done without a proper PLC restart sequence
Triage note: Official reaction: PLC STOP; program continuation 'Switch control OFF - ON'. Valid for powerline and solutionline.
Need the part urgently?
Send us alarm 400201 with your machine details — typical RFQ turnaround is 24–48h.