Error Message Reference

The following table maps common S7 error strings to their likely cause and fix.

Error message	Likely cause	Fix
CLI : function refused by CPU (Unknown error)	PUT/GET communication is not enabled on the PLC, or the data block still has optimized block access enabled.	Enable PUT/GET in TIA Portal and disable optimized block access on each DB. See TIA Portal Configuration.
CPU : Function not available	The requested function is not supported on this PLC model. S7-1200 and S7-1500 PLCs restrict certain operations.	Check Siemens documentation for your PLC model. Some functions are only available on S7-300/400.
CPU : Item not available	Wrong DB number, the DB does not exist, or the address is out of range.	Verify the DB number exists on the PLC and that the offset and size are within bounds.
CPU : Address out of range	Reading or writing past the end of a DB or memory area.	Check the DB size in TIA Portal and ensure start + size does not exceed it.
CPU : Function not authorized for current protection level	The PLC has password protection enabled.	Remove or lower the protection level in TIA Portal under Protection & Security.
ISO : An error occurred during recv TCP : Connection timed out	Network issue: PLC is unreachable, a firewall is blocking port 102, or the PLC is not responding.	Check network connectivity (ping), verify firewall rules, and ensure the PLC is powered on and reachable.
ISO : An error occurred during send TCP : Connection timed out	Same as above.	Same as above.
TCP : Unreachable peer	The PLC is not reachable on the network.	Verify IP address, subnet, and routing. Ensure the PLC Ethernet port is connected and configured.
TCP : Connection reset / Socket error 32 (broken pipe)	The connection to the PLC was lost unexpectedly.	The PLC may have been restarted, the cable disconnected, or another client took over the connection. See Connection Issues.