What causes FANUC alarm 338?

Machine system or function indicated by the alarm name has detected a fault. Control parameter or configuration error related to the alarm condition. Hardware component fault on the CNC or machine. Part program error or illegal operation for the indicated function. Machine interlock or safety condition not satisfied.

How do I fix FANUC alarm 338?

1. Note the alarm number and check the Fanuc alarm screen for any sub-code or additional details. 2. Identify the specific machine system or function from the alarm name. 3. Power cycle the machine to clear transient faults. 4. Consult the Fanuc parameter or operator manual for alarm 338 specific remedy. 5. Contact Fanuc service if the alarm persists after basic troubleshooting.

axismd.ai

FANUC Controller

Program/G-code · Intermediate · 20-45 minutes

Alarm 338

Fanuc Alarm 338 - ILLEGAL EXEC SEQUENCE OF BLOCK

Alarm 338 ILLEGAL EXEC SEQUENCE OF BLOCK indicates the CNC has detected an improper execution order or corrupted program block structure, typically caused by CNC memory corruption, improper program editing/transfer, or system-level data integrity issues. This alarm is part of Fanuc's malfunction prevention function that monitors internal execution sequences and checksums to prevent erratic machine behavior.

FANUCProgram/G-codeIntermediate20-45 minutes

338

Fanuc Alarm 338 - ILLEGAL EXEC SEQUENCE OF BLOCK

SYSTEM ALARM 338

Root Cause Summary

Alarm 338 ILLEGAL EXEC SEQUENCE OF BLOCK indicates the CNC has detected an improper execution order or corrupted program block structure, typically caused by CNC memory corruption, improper program editing/transfer, or system-level data integrity issues. This alarm is part of Fanuc's malfunction prevention function that monitors internal execution sequences and checksums to prevent erratic machine behavior.

Causes and Fixes

1
Check battery voltage at SYSTEM > MAINTENANCE > BATTERY screen. Voltage should be above 3.0V for lithium batteries. On 0i/30i/31i/32i systems, also check DIAGNOSIS #197 (battery alarm status). Replace battery if below 3.0V.
Power must remain ON during battery replacement to prevent total memory loss. Have parameter backup ready.
2
Reset the alarm and reload the program from proven backup. Delete the corrupted program completely using MDI or memory card before reloading to clear memory address conflicts.
3
Perform memory clear (Parameter clear: Parameter 0000 set to 1 with key switch in EMERGENCY position, power cycle). Reload all parameters from backup, then test program execution.
This erases all parameters, offsets, and programs. Only perform if you have complete system backup.
4
If alarm persists after memory clear, check CF card or FROM module integrity. Access SYSTEM > MAINTENANCE > LIFE to check flash memory health status on 30i/31i/32i systems. Replace if write count approaching limit.

DIY Feasiblehigh confidence

Call a technician if:

·Memory test fails
·Parameter restoration doesn't resolve alarm
·Hardware replacement needed

Prevention

Regular battery voltage monitoring
Maintain clean program backups
Use error-checking during program transfers
Implement UPS for power stability

Common Mistakes

Ignoring low battery warnings
Transferring programs without verifying communication settings
Not backing up parameters before changes
Using damaged network cables

Related Alarms

078 900 999

Seeing Multiple Alarms?

Seeing another alarm with this one? Enter the code.

Get machine-aware diagnosis

AxisMD logs alarms against your actual machines, tracks patterns, and gives AI context your manual doesn't have.

Start free

Was this guide helpful?

Always verify with your machine manual or a certified technician before performing service procedures.