Technician operating FANUC CNC testing benches during system inspection and repair at REACO CNC.

FANUC Alarm Code Guide

Find solutions to common Fanuc CNC alarm codes quickly and efficiently.

Servo Alarm
Spindle Alarm
System Alarm
Overtravel Alarm

FANUC Alarms: Quick Guide to Get Back Online​

When your FANUC CNC triggers an alarm, it's trying to tell you something. From simple overtravel to complex servo issues, these codes pinpoint where the problem lies.Our guide cuts through the complexity. We explain the most common alarms—what they mean, why they happen, and how to fix them. Whether you're facing alarm 401 or a stuck overtravel limit, you'll find clear, step-by-step solutions to minimize downtime.​​ You will learn how to:​​

  • Decode any FANUC alarm number.
  • Diagnose faults in servos, spindles, or system memory.
  • Perform basic checks before calling a technician.
  • Identify components that may need adjustment or replacement.

Get the knowledge to solve problems faster and keep your machines running.
FANUC SV0463 Alarm: Slave Data Transmission Error
The FANUC SV0463 alarm indicates a slave data transmission error. This alarm occurs when the servo software side cannot receive correct data because of an FSSB communication error. FSSB, also known as Fanuc Serial Servo Bus, is the communication system between the CNC control unit and the servo amplifier system. If the FSSB parameters are not set correctly, the optical fiber cable is damaged, the cable is connected incorrectly, or the amplifier control board has poor contact, the servo software may not receive valid data and the CNC system may... Read more...
FANUC SV0462 Alarm: CNC Data Transmission Error
The FANUC SV0462 alarm indicates a CNC data transmission error. This alarm occurs when the amplifier cannot receive correct data from the control unit because of an FSSB communication error. FSSB, also known as Fanuc Serial Servo Bus, is used for communication between the CNC control unit and the servo amplifier system. If the FSSB optical fiber cable is damaged, loose, disconnected, connected incorrectly, or if the amplifier control board has poor contact, the data sent from the CNC may not be received correctly by the drive side. In this... Read more...
FANUC SV0460 Alarm: FSSB Communication Disconnected
The FANUC SV0460 alarm indicates an FSSB communication disconnected condition. This alarm occurs when the CNC system detects that FSSB communication has been interrupted or disconnected. FSSB, also known as Fanuc Serial Servo Bus, is the communication path between the CNC and servo amplifier system. If the optical fiber cable is loose, damaged, disconnected, or if an amplifier loses control power, the CNC may lose communication with the drive system and generate the SV0460 alarm. SV0460 is not always caused by a broken FSSB cable itself. In some cases, it... Read more...
FANUC SV0449 Alarm: Inverter IPM Alarm
The FANUC SV0449 alarm indicates an inverter IPM alarm. This alarm occurs when the servo amplifier IPM, also called the Intelligent Power Module, detects an abnormal condition. The IPM is an important power module inside the servo amplifier. It controls the power output to the servo motor and monitors abnormal current, short circuit, power module fault, and related drive conditions. If the IPM detects an abnormal condition, the CNC system may generate the SV0449 alarm. In many cases, SV0449 is caused by a motor short circuit, motor power cable ground... Read more...
FANUC SV0448 Alarm: Feedback Mismatch
The FANUC SV0448 alarm indicates a feedback mismatch alarm. This alarm occurs when the sign of the feedback data from the built-in pulse encoder is opposite to the sign of the feedback data from the external detector. SV0448 is usually related to a full-closed loop control system. In this type of system, the CNC uses both the servo motor built-in pulse encoder and an external detector, such as a linear scale or external encoder, to monitor axis movement. The feedback direction from both devices must be consistent. If the built-in... Read more...
FANUC SV0447 Alarm: Hard Disconnection External Detector
The FANUC SV0447 alarm indicates a hard disconnection alarm for the external detector. This alarm occurs when hardware detects a disconnection in the external detector feedback circuit. SV0447 usually occurs in a full-closed loop system, where the CNC system uses an external detector such as a linear scale, external encoder, or rotary encoder to detect the actual machine position. If the external detector signal is interrupted, the feedback cable is disconnected, the connector is loose, or the detector itself is faulty, the CNC system may generate the SV0447 alarm. Unlike... Read more...
FANUC SV0446 Alarm: Hard Disconnection Alarm
The FANUC SV0446 alarm indicates a hard disconnection alarm. This alarm occurs when hardware detects a disconnection in the built-in pulse encoder. The built-in pulse encoder is used to send motor feedback signals to the servo system. If the encoder feedback signal is interrupted, the encoder connector is loose, the motor feedback cable is damaged, or the encoder itself is faulty, the CNC system may generate the SV0446 alarm. Unlike SV0445, which is detected by digital servo software as a soft disconnection alarm, SV0446 is detected by hardware. Therefore, troubleshooting... Read more...
FANUC SV0445 Alarm: Soft Disconnection Alarm
The FANUC SV0445 alarm indicates a soft disconnection alarm. This alarm occurs when the digital servo software detects a disconnection in the pulse encoder signal. SV0445 is commonly seen in full-closed loop systems using an external detector, such as a linear scale, external pulse encoder, or rotary encoder. It belongs to an external detector pulse encoder alarm. When the CNC system detects an abnormal feedback signal or possible encoder disconnection, the SV0445 alarm may appear. This alarm may be caused by incorrect parameter settings, feedback cable disconnection, poor connector contact,... Read more...
FANUC SV0444 Alarm: Inverter Cooling Fan Failure
The FANUC SV0444 alarm indicates an inverter cooling fan failure. This alarm occurs when the servo amplifier detects that the internal cooling fan motor used to cool the amplifier has stopped or is operating abnormally. The internal cooling fan helps remove heat from inside the servo amplifier. If the fan is not installed, not inserted correctly, blocked by foreign objects, contaminated by oil or dust, or physically damaged, the amplifier may detect a cooling fan failure and generate the SV0444 alarm. SV0444 is usually related to the internal cooling fan... Read more...
FANUC SV0443 Alarm: Inverter Cooling Fan Failure
The FANUC SV0443 alarm indicates an inverter cooling fan failure. This alarm occurs when the system detects an abnormal condition in the internal cooling fan of the amplifier or power supply module. In many FANUC servo systems, the power supply module or amplifier uses an internal cooling fan to remove heat from the module. If the fan is not installed, not connected correctly, blocked by contamination, or damaged, the module may report SV0443 to protect the drive system from overheating. According to the troubleshooting condition, this alarm may be related... Read more...
FANUC SV0442 Alarm: DC Link Charging Abnormal in Inverter
The FANUC SV0442 alarm indicates a DC link charging abnormal condition in the inverter. This alarm occurs when the common power supply detects an abnormal condition in the DC link backup discharge circuit or when the drive cannot charge the main circuit within the specified time after emergency stop is released. In a FANUC servo system, the DC link circuit must be charged correctly after the machine power sequence is enabled. If the main power is not supplied in time, the voltage is insufficient, the phase sequence is incorrect, the... Read more...
FANUC SV0441 Alarm: Abnormal Current Offset
The FANUC SV0441 alarm indicates an abnormal current offset. This alarm occurs when the digital servo software detects an abnormal condition in the motor current detection circuit. The motor current detection circuit is used by the servo amplifier to monitor the current supplied to the servo motor. If the detected current signal is abnormal, offset, or outside the expected condition, the CNC system may generate the SV0441 alarm. In many cases, this alarm is related to servo amplifier hardware failure. If the amplifier current detection circuit is damaged, the alarm... Read more...

Related Resources

Explore more technical materials to help you troubleshoot, maintain, and optimize your CNC system.

Related Links List：

Back to Main Technical Support
Close-up of a CNC machine cutting aluminum parts with high precision.

Need Technical Support or Repairs?

We offer repair services for all CNC parts, including systems, drives, motors, encoders, and PCBs. Fast repair, full testing, and REACO CNC warranty included. Contact us for guidance, troubleshooting, parameter support or repair.

 Tech Support