How to Remove Write Protection on a Fanuc CNC — PWE, Memory Protect Keys & Locked Programs

“Write protected” on a Fanuc control is not one setting — it is several independent locks, and the fix depends on which one is stopping you. This guide covers all of them for 0i, 16i/18i/21i, 30i/31i/32i and 0i-F controls: the PWE parameter-write switch, the memory protect key signal, program protection bits in parameter 3202, and the 8-level protection system on newer controls.

First: what exactly is blocked?

• Cannot change parameters (‘WRITE PROTECT’ when editing a parameter) → PWE is off. See Case 1.
• Cannot edit or delete part programs (‘edit rejected’, programs greyed out) → memory protect key or parameter 3202. See Cases 2 and 3.
• Cannot edit O8000/O9000-series programs specifically → they are locked on purpose. See Case 3.
• Cannot change offsets or settings → memory protect key signal. See Case 2.

Case 1 — Enable parameter writing (PWE)

1. Select MDI mode.
2. Press OFS/SET → [SETTING] softkey to open the setting screen.
3. Move the cursor to PARAMETER WRITE and set it to 1.
4. Alarm SW0100 ‘Parameter write enable’ appears — this is normal and stays on while writing is enabled.
5. Make your parameter change, then set PARAMETER WRITE back to 0 and press RESET to clear the alarm.

Case 2 — Memory protect key (KEY switch)

Machine builders wire a physical keyswitch (or an OEM soft key) to the control's memory-protect signals (KEY1–KEY4). Depending on the builder, these lock program edit, offsets, settings and macro variables.

1. Look for a keyswitch on the operator panel labelled PROGRAM PROTECT / EDIT KEY / MEMORY PROTECT and turn it to the unlocked position.
2. No physical key? Some builders put it on a custom soft-panel screen instead — check the builder's operation manual.
3. If the switch seems ON but editing is still blocked, the keyswitch contact or its input signal may be faulty — an electrician can verify the KEY signal state on the PMC diagnosis screen (PMCDGN → STATUS, addresses per the builder's ladder documentation).

Case 3 — Program protection bits (parameter 3202)

Parameter 3202 controls editing of protected program ranges:

• Bit 0 (NE8) = 1 → programs O8000–O8999 cannot be edited, displayed or deleted.
• Bit 4 (NE9) = 1 → programs O9000–O9999 (usually the builder's macro programs) are locked and hidden.

1. Enable PWE (Case 1).
2. Open parameter 3202 and set NE8 or NE9 to 0 as needed.
3. Set PWE back to 0. The programs now appear in the directory and can be edited.

Case 4 — 8-level protection (0i-F / 30i-series)

Newer controls add an 8-level access system (operation levels 0–7) that can independently protect parameters, programs and offsets per level.

1. Press SYSTEM → [+] → [PROTECT] to open the protection setting screen.
2. Log in at a higher level (default passwords are set by the builder; level 4–7 items need the corresponding login).
3. Adjust the change-permission level for the data type you need, make the edit, then log out.

Still locked?

• Alarm 100 will not clear — PWE still 1 somewhere, or on 2-path lathes, set PWE on both paths.
• Edits accepted but lost after power-off — the control is not saving: CMOS battery flat (see our battery guide) or memory board fault.
• ‘WRITE PROTECT’ on data input via RS-232/card — check setting screen item TVC/ISO and the I/O channel, and that the target program number range is not NE8/NE9-locked.

Related guides

• How to back up Fanuc parameters (0i/16i/18i/30i)
• Fanuc reference position / zero return guide
• Fanuc PS5523/PS5524 certification alarm removal