What causes FANUC alarm 028?

Part program contains an illegal or malformed command related to the alarm condition. Missing required address word or parameter value in the program block. Programmed value is out of the allowable range. Conflict between active modal codes and the commanded function. Post-processor configuration mismatch for this Fanuc series.

How do I fix FANUC alarm 028?

1. Note the block number shown in the alarm screen and locate that block in the program. 2. Review the command in that block against the Fanuc programming manual. 3. Check for missing words, incorrect values, or conflicting G-code combinations. 4. Verify the program is post-processed for the correct Fanuc series. 5. Correct the program and dry-run at low speed before resuming machining.

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FANUC Controller

Program/G-code · Basic · 5-15 minutes

Alarm 028

Fanuc Alarm 028 - Protected Data Write Attempt

Fanuc Alarm 028 occurs when the CNC attempts to write data to a memory area that is write-protected, typically parameters, offset data, or macro variables that have been locked via parameter settings or KEY switch position. This protection prevents unauthorized or accidental modification of critical machine configuration data.

FANUCProgram/G-codeBasic5-15 minutes

028

Fanuc Alarm 028 - Protected Data Write Attempt

Protect Data Illegal

Root Cause Summary

Fanuc Alarm 028 occurs when the CNC attempts to write data to a memory area that is write-protected, typically parameters, offset data, or macro variables that have been locked via parameter settings or KEY switch position. This protection prevents unauthorized or accidental modification of critical machine configuration data.

Safety

Data cannot be modified

Causes and Fixes

1
Check the front panel KEY switch position. For most Fanuc controls, turn KEY switch to position 1 or higher to enable parameter writing. On some controls without physical key switch, verify software key switch setting.
2
Navigate to SYSTEM > PARAM screen. Press SETTINGS soft key and verify parameter write enable status is displayed at top of screen (should show 'ENABLE' or 'PWE' indicator lit).
3
Check parameter 3202#0 (PWE). Navigate to SYSTEM > PARAM, input parameter number 3202, verify bit 0 = 1 to enable parameter writing. If set to 0, change to 1 with KEY switch in correct position.
Changing parameter 3202#0 requires control power cycle to take effect. Document all parameter changes per machine safety procedures.
4
After enabling write protection override, retry the operation that triggered alarm 028. Press RESET button to clear alarm after protection is properly disabled.

DIY Feasiblehigh confidence

Call a technician if:

·Parameter backup corruption
·Persistent alarms after program correction
·Suspected control hardware issues

Prevention

Always specify plane selection explicitly in programs rather than relying on modal states
Use consistent plane selection throughout program sections
Validate programs in simulation mode before production runs
Maintain parameter backup files for quick restoration

Common Mistakes

Assuming G17 is default plane selection on startup
Changing planes while cutter compensation is active
Using incorrect I,J,K parameters for selected plane
Missing tool length compensation before radius compensation

Related Alarms

010 011 020 029 033

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