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Press RESET to clear the alarm. Navigate to EDIT mode and review the current program where the alarm occurred.

Search for M99 commands in the program using the search function. Verify each M99 is within a subprogram (not the main O-number program being executed).

If M99 is found in the main program, either remove it or replace it with M30 (program end) or M02 (program end without reset) as appropriate for main program termination.

If the intent was to create a repeating loop in the main program, use M99 P[line_number] to jump to a specific line, or restructure the program to use proper subprogram calls with M98.

M99 P___ for looping in main programs may not be supported on all Fanuc control versions. Verify compatibility with parameter 3404 bit 5 (M99 loop enable) if available on your series.

Verify the correct program is selected for execution. Check that the main program O-number is the intended calling program, not the subprogram containing M99.

Trace through the program logic to confirm M98 P[subprogram_number] exists before the subprogram with M99 is expected to execute. Check for optional block skip characters (/) that may bypass the M98 call.

Verify parameter 3404 bit 0 (subprogram call method) is set correctly for your programming style. Navigate to SYSTEM > PARAM and check parameter 3404.

Changing parameter 3404 requires parameter write enable (parameter 0000 bit 0 = 1). Set bit back to 0 after modification to protect parameters.

If using macro variables or conditional calls (IF statements), verify the program flow logic ensures M98 is executed before reaching M99. Test in single block mode (SINGLE BLOCK button ON) to trace execution.

Check the maximum nesting level for your control series. For most Fanuc systems: 0i/16i/18i support 4 levels, 30i/31i/32i support 8-16 levels depending on options. Count M98 nesting depth in your program.

Power cycle the CNC control (EMERGENCY STOP, power OFF for 30 seconds, power ON) to clear any corrupted call stack memory. Navigate to SYSTEM > DIAGNOSIS > 300-399 after restart to check for subprogram nesting level status.

Ensure all axes are at safe positions and machine is clear before power cycling. Coordinate with machine operator.

Restructure deeply nested subprograms by consolidating logic or using macro programming (G65) if available, which has separate nesting limits. Review parameter 6008 (macro nesting level) if applicable.

If problem persists after restructuring, backup all programs and parameters, then perform a control memory clear (ALL CLEAR initialization) and reload programs. This resolves potential memory corruption issues.

ALL CLEAR erases all programs, parameters, offsets, and PMC ladder. Only perform with complete backup and OEM support. Requires battery-backed memory or CF card restore capability.