After identification is complete or parameters are changed, save the settings by performing a copy (set P0971 = 1 ). This ensures the alarm does not return after a power cycle. Common Troubleshooting Scenarios
A missing termination resistor on PROFIBUS, a damaged connector, or a faulty switch on PROFINET can cause intermittent communication with a remote I/O device. When the CPU attempts to read or write to that device, it triggers the I/O access error. siemens fault 0a7991