Okuma Alarm A-1091 – PLC Alarm Message File Not Found
What Does Alarm A1091 Mean?
The Okuma alarm A1091 indicates that the PLC alarm message file cannot be located by the control system. This file contains the text definitions for PLC-generated alarms. If it is missing or corrupted, the control may still detect PLC faults, but the corresponding alarm messages will not be displayed correctly.
As a result, normal alarm processing may be partially disabled, and diagnostic information may be incomplete.
Technical Background
Okuma CNC controls use PLC (Programmable Logic Controller) data files to manage machine logic, interlocks, and alarm messages. The alarm message file stores readable text corresponding to PLC alarm codes.
If this file is:
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Deleted
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Corrupted
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Located in the wrong directory
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Unreadable due to storage failure
the control cannot properly interpret or display PLC alarm messages.
In many cases, this issue is related to:
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Hard disk or CF card degradation
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Incomplete software installation
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Interrupted system update
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File system corruption
Typical Symptoms
When Alarm A1091 appears, operators may notice:
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PLC alarms without readable text
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Missing alarm descriptions
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Abnormal alarm behavior
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Startup interruptions
The machine may still power on, but diagnostic clarity is reduced.
Possible Causes
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Missing PLC alarm message file
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Corrupted system data
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Storage media failure (HDD / CF card)
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Improper software update
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Incorrect system data restoration
Recommended Troubleshooting Steps
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Verify whether the PLC alarm message file exists in the system directory
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Restore the file from a verified backup
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Check storage media condition
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Reinstall PLC system data using official Okuma procedures
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Perform hardware diagnostics if storage issues are suspected
⚠️ Important: Avoid copying system files from unofficial sources, as version mismatches may cause further instability.
When Professional Repair Is Required
If the alarm persists after file restoration, the problem may be hardware-related. Common hardware causes include:
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Failing CF card
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Damaged HDD
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Control board communication issues
Our CNC electronics specialists provide:
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Okuma control diagnostics
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PLC data recovery
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Storage device replacement
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Board-level electronic repair
FAQ
Can the machine run with Alarm A1091 active?
In most cases, limited operation may be possible, but alarm messages will not be displayed correctly. This significantly complicates troubleshooting and should not be ignored.
Is this a PLC programming error?
No. Alarm A1091 is typically related to missing system files, not user PLC programming.
