Siemens SIMATIC S7-1500 System Manual page 190

Diagnostics
System state, operating states and error displays after the failure of both PROFINET cables on
the backup CPU:
• Redundant system → RUN-Redundant system state
• Primary CPU/Backup CPU → RUN-Redundant operating state
– MAINT LED → yellow light: The PROFINET ring is open. No backup AR.
Note
To get detailed diagnostics information, evaluate the diagnostics buffer.
Solution
Replace the defective PROFINET cables. You can find additional information on the procedure
in the section Replacing defective PROFINET cables (Page 451).
S7-1500R/H redundant system
System Manual, 01/2024, A5E41814787-AF
Application planning
6.4 Redundancy scenarios
189