WARNING: Improper setting of Parameter 8901 can result in servo alarms, overrun errors, or collision with the workpiece.
Procedure:
In FANUC CNC systems, Parameter 8901 is primarily used to control how the system monitors and reacts to fan motor errors. It is most commonly referenced during troubleshooting for a 701 Fan Motor Overheat Alarm. Key Functionality
Bit 0 (FAN): This bit determines whether the CNC monitors the cooling fans within the control unit.
Set to 0: Monitoring is active. If a fan motor fails or runs too slowly, the system triggers an alarm (like Alarm 701) and often stops the machine to prevent overheating.
Set to 1: Monitoring is disabled. This suppresses the fan error alarm, allowing the machine to run even if a fan fault is detected. When to Adjust Parameter 8901
While changing this parameter can clear an immediate alarm, it should be done with caution:
Temporary Troubleshooting: If you receive a 701 alarm, setting 8901 bit 0 to "1" can help confirm if the control unit is still operational or allow you to finish a critical cycle. fanuc parameter 8901 better
Safety Warning: Disabling this check is not a permanent fix. Running the CNC without functional fans can lead to critical overheating and expensive damage to printed circuit boards or other hardware components.
Recommended Action: Instead of permanently disabling the alarm, it is safer to replace the faulty fan motors immediately. Related Alarms and Context
Alarm 701: Specifically indicates that a fan in the CNC control unit (not the spindle or external cabinet) has failed.
Maintenance: On modern systems like the Series 30i/31i/32i, these fans are considered "maintenance parts" that should be periodically inspected and replaced as they age. FANUC Series 30i/31i/32i-MODEL B MAINTENANCE MANUAL
In the complex ecosystem of FANUC CNC systems Parameter 8901
serves as a vital safeguard—and occasionally a temporary workaround—for maintaining the thermal integrity of the control unit. Specifically, this parameter is tied to the monitoring of the system cooling fans The Role of Parameter 8901 When a FANUC control (such as the
) detects that a cooling fan has slowed down or failed, it triggers WARNING: Improper setting of Parameter 8901 can result
. This alarm is a critical warning; without proper airflow, the internal electronic components of the CNC can overheat, leading to hardware failure or data corruption. Parameter 8901 bit 0 (often written as ) controls the system's response to this fan error: Setting 0 (Standard):
The CNC monitors the fan speed. If a failure is detected, Alarm 701 is issued, often stopping the machine to prevent heat damage. Setting 1 (Shielding):
This setting "shields" or suppresses the alarm, allowing the machine to continue operating even if the fan signal is missing or faulty. Using the Parameter "Better" While setting 8901#0 to 1
can clear a stubborn alarm, it should never be viewed as a permanent "fix." To manage this parameter better, follow these strategic steps: Temporary Troubleshooting:
Use the shielding bit only to diagnose if the alarm is coming from the System Fan (control unit) rather than the Servo Fans
(located on the drive amplifiers). If the alarm disappears after changing 8901, the issue is definitively with the control unit fan. Emergency Production:
If a replacement fan is unavailable and production must continue, you can set the parameter to 1, but you forced air cooling In FANUC CNC systems, Parameter 8901 is primarily
(e.g., leaving the cabinet door open with an external fan) to prevent the CNC from burning out. Restoration: Once the hardware is replaced, immediately revert Parameter 8901#0 back to 0
. Operating permanently with the alarm shielded leaves the system vulnerable to catastrophic overheating without warning. How to Change the Parameter To modify this setting, you must first enable Parameter Write Enable (PWE) Set the machine to soft key and set PARAMETER WRITE Navigate to Parameter 8901 and change the first bit (far right) to the desired value. Once finished, set PARAMETER WRITE to clear any remaining I/O alarms. Machine Metrics fan part numbers for your Fanuc series to order a replacement? FANUC fan alarm troubleshooting - Knowledge - Jide
1 System fan, 701 alarm, 8901#0 parameter is changed to 1 to temporarily shield the alarm (OIC system); Dongguan Jide Precision Machinery Technology Co., Ltd. How to Enable Parameter Write Enable (PWE) on a Fanuc CNC
The parameter 8901 on FANUC controls (especially Series 0i, 16i, 18i, 21i, and later) is a bit-data type parameter used to define rotation/shortcut axis (RoTary axis) assignment and its related reference position return behavior.
Here is the breakdown of FANUC Parameter 8901:
When 8901=1 (AICC I), the machine looks ahead and blends corners. This is decent, but it uses a linear acceleration profile. In high-feed applications (over 200 IPM), the control can "overshoot" tiny segments, causing servo lag.
| Method | Repeatability | Maintenance | Speed | Thermal Stability | |--------|---------------|-------------|-------|-------------------| | Dog + grid (8901.0=0) | ±5–10 µm | High (dog wear) | Slow | Poor (dog changes with temp) | | Dogless (8901.0=1, bits 4&7=1) | ±0.5–1 µm | None | Fast | Excellent (direct to encoder) |
The “better” setting eliminates mechanical hysteresis and improves long-term consistency.