Watchdog or RAM Parity Error

What does 921 mean?

These alarms indicate either a watchdog timer error or a RAM parity error within the Fanuc Series 20 CNC. A watchdog error signifies that the CPU is not executing its regular cycle, possibly due to a program loop or freeze, while a RAM parity error indicates data corruption in memory. Both lead to system instability or halt.

• Software malfunction or program crash causing the CPU to hang (watchdog).
• Faulty CPU or other main board components (watchdog).
• Faulty RAM module(s) or memory interface (RAM parity).
• Transient power fluctuations or electrical noise affecting the CPU or memory.
• External interrupt or I/O issue leading to system freeze.

Click steps to track your progress.

1. 1

   Power cycle the CNC completely to reset the CPU and clear any transient software or memory states.

2. 2

   Verify stable and clean power supply to the CNC main unit and inspect for any visible damage to the main board.

3. 3

   Check for any recent software updates, parameter changes, or new programs that might have introduced instability.

4. 4

   If multiple RAM modules are present, attempt to reseat them or test them individually if the error is identified as RAM parity.

5. 5

   If the alarm persists and no other specific fault is identified, the CNC main board (CPU/memory area) may be faulty and require replacement.