Code 201039: <location>ACX: Writing to the parameter back-up file was unsuccessful
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>ACX: Writing to the parameter back-up file was unsuccessful alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Message value: %1 Drive object: All objects Reaction: A_INFEED: NONE (OFF2) SERVO: NONE (OFF1, OFF2, OFF3) VECTOR: NONE (OFF1, OFF2, OFF3) Acknowledge: IMMEDIATELY Cause: Writing to at least one parameter back-up file PSxxxyyy.*** on the CompactF lash card was unsuccessful. - on the CompactFlash card in the directory /USER/SINAMICS/DATA/ at least one parameter backup file PSxxxyyy.*** has the "read only" file attribute and cannot be overwritten. - there is not sufficient free memory space on the CompactFlash card. - the CompactFlash card is defective and cannot be written to. Fault value (r0949, interpret hexadecimal): dcba hex a = yyy in the file names PSxxxyyy.*** a = 000 --> consistency back-up file a = 001... 062 --> drive object number a = 099 --> PROFIBUS parameter back-up file b = xxx in the file names PSxxxyyy.*** b = 000 --> data save started with p0977 = 1 b = 010 --> data save started with p0977 = 10 b = 011 --> data save started with p0977 = 11 b = 012 --> data save started with p0977 = 12 d, c: Only for internal Siemens troubleshooting. Remedy: - check the file attribute of the files (PSxxxyyy.***, CAxxxyyy.***, CCxxxyy y.***) and, if required, change from "read only" to "writeable". - check the free memory space on the CompactFlash card. Approx. 40 kbyte of free memory space is required for every drive object in the system. - replace the CompactFlash card.
Source: SINUMERIK 840D sl / 840Di sl / SINAMICS S120 Diagnostics Manual (DAsl, 03/2009)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Siemens SINUMERIK 840D CNC Alarms
Siemens controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 201039 on the SINUMERIK 840D CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Siemens's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4014 Siemens SINUMERIK 840D CNC codes.
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