Siemens alarm 400552: Fault on DP bus
SINUMERIK PLC system alarm · Siemens 840D/810D powerline
What it means
An error was detected on the PROFIBUS-DP I/O bus connecting the PLC to its distributed I/O. While this alarm stands, outputs/inputs transported over the failing segment cannot be trusted, which typically blocks machine function chains that depend on them. Locate the failing station with STEP 7/NCU bus diagnostics and repair the physical bus or the slave.
Likely causes
- DP slave failure or power loss
- Cable break, loose connector or missing termination resistor
- Configuration/baud-rate mismatch after hardware changes
Triage note: Detailed per-slave diagnostics surface as the 4286xx alarm family; 428604 covers single DP slave failure.
Need the part urgently?
Send us alarm 400552 with your machine details — typical RFQ turnaround is 24–48h.