What causes FANUC alarm 118?

Complex macro arithmetic expression with more levels of nested brackets than allowed. Macro expression has more than 5 levels of nested brackets (typical Fanuc limit). Recursive macro structure creating excessive bracket nesting. Expression copied from a system with a higher nesting limit.

How do I fix FANUC alarm 118?

1. Locate the macro expression at the alarm block and count the bracket nesting levels. 2. Simplify the expression by splitting it into multiple assignment steps using intermediate variables. 3. Reduce nesting depth to within the Fanuc limit (typically 5 levels). 4. Test the simplified expression with known values before running the full program.

axismd.ai

FANUC Controller

Program/G-code · Advanced · 30-60 minutes

Alarm 118

Fanuc Alarm 118 - TOO MANY BRACKET NESTING

Alarm 118 indicates that the CNC has detected corruption in the program memory (RAM or SRAM). This typically occurs due to battery failure causing data loss during power-off, electrical noise/interference affecting memory integrity, or hardware failure of the memory module or main PCB. The system performs checksum verification on stored data and triggers this alarm when mismatches are detected.

FANUCProgram/G-codeAdvanced30-60 minutes

118

Fanuc Alarm 118 - TOO MANY BRACKET NESTING

TOO MANY BRACKET NESTING

Root Cause Summary

Alarm 118 indicates that the CNC has detected corruption in the program memory (RAM or SRAM). This typically occurs due to battery failure causing data loss during power-off, electrical noise/interference affecting memory integrity, or hardware failure of the memory module or main PCB. The system performs checksum verification on stored data and triggers this alarm when mismatches are detected.

Safety

Programs may be lost

Causes and Fixes

1
Check battery voltage at DIAGNOSIS screen > STATUS > BATTERY. Verify absolute encoder battery shows above 3.0V and main battery above 3.2V. On older systems, access via SYSTEM > DIAGNOSIS > #196 (battery voltage).
2
Inspect physical battery condition on the main PCB and servo amplifier. Look for corrosion, swelling, or date code indicating age over 5 years. Replace batteries immediately if voltage is low or physical damage present.
Always perform controlled shutdown and maintain AC power when replacing main CPU battery to prevent total memory loss. Have backup files ready.
3
After battery replacement, restore all parameters from backup using SYSTEM > PMC > I/O or memory card restore function. Verify parameter set with OEM documentation.
4
Clear alarm by power cycling the control. Re-establish reference position for all axes (return to zero). Verify PMC ladder program and all macro variables are intact.

DIY Feasiblehigh confidence

Call a technician if:

·Memory corruption persists after program reload
·Parameter corruption affects multiple system functions
·Hardware memory failure suspected

Prevention

Limit macro nesting to maximum 4 levels
Use subroutines instead of deep nesting
Regular macro program backup
Validate macro syntax before execution

Common Mistakes

Counting only IF statements without including function brackets
Ignoring recursive call depth in nesting calculation
Not backing up programs before editing
Mixing different bracket types incorrectly

Related Alarms

126 127 128 129

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.