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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 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...
FANUC SV0440 Alarm: Excessive Deceleration Power
The FANUC SV0440 alarm indicates that the deceleration power is too large. This alarm occurs when the regenerative discharge amount of the common power supply or servo amplifier becomes excessive, or when the regenerative discharge circuit is abnormal. During servo motor deceleration, the motor returns energy back into the drive system. This regenerated energy must be properly discharged through the regenerative discharge circuit or regenerative resistor. If the deceleration energy is too high, the regenerative resistor is not connected correctly, the regenerative discharge circuit is abnormal, or the resistor capacity... Read more...
FANUC SV0439 Alarm: Inverter DC Link Overvoltage
The FANUC SV0439 alarm indicates an inverter DC link overvoltage condition. This alarm occurs when the voltage of the DC section of the main circuit, also called the DC bus or DC link, becomes abnormally high. In a FANUC servo system, the servo amplifier and common power supply require stable main circuit voltage. If the DC link voltage rises above the allowable range, the CNC system may generate the SV0439 alarm to protect the servo amplifier, common power supply module, and connected servo system. This alarm may be caused by... Read more...
FANUC SV0438 Alarm: Inverter Current Abnormal
The FANUC SV0438 alarm indicates an inverter current abnormal condition. This alarm occurs when the CNC system detects abnormal motor current or excessive current in the servo motor circuit. In normal servo operation, the motor current should remain within the allowable range for the servo motor, servo amplifier, and machine load condition. If the motor current becomes too high, or if the servo amplifier detects an abnormal current condition, the system may generate the SV0438 alarm. This alarm may be caused by abnormal machining load, excessive acceleration or deceleration, incorrect... Read more...
FANUC SV0437 Alarm: Inverter Input Circuit Overcurrent
The FANUC SV0437 alarm indicates an inverter input circuit overcurrent condition. This alarm occurs when overcurrent is detected in the input circuit of the common power supply, also called the PS module. In a FANUC servo system, the common power supply module supplies power to the servo amplifier system. If excessive current flows into the main input circuit of the common power supply, the CNC system may generate the SV0437 alarm. In some cases, the common power supply may display alarm code 1. This alarm may be related to insufficient... Read more...
FANUC SV0435 Alarm: Inverter DC Link Low Voltage
The FANUC SV0435 alarm indicates an inverter DC link low voltage condition. This alarm occurs when the DC link voltage, also called the DC bus voltage, inside the servo amplifier drops below the required level. In a FANUC servo system, the servo amplifier depends on a stable DC bus voltage for normal inverter operation. If the DC link connection is loose, the wiring is incorrect, the DC bus connection cable or bus bar is not properly tightened, the amplifier control circuit board is not inserted correctly, or the servo drive... Read more...
FANUC SV0434 Alarm: Inverter Control Voltage Low
The FANUC SV0434 alarm indicates an inverter control voltage low condition. This alarm occurs when the control power voltage of the servo amplifier drops below the required level. The servo amplifier requires a stable control power supply for normal operation. If the control voltage becomes too low, the CNC system may detect an abnormal amplifier control power condition and generate the SV0434 alarm. This alarm may be related to abnormal DC24V output from the common power supply, incorrect jumper cable connection between servo amplifiers, feedback cable problems, external control circuits... Read more...
FANUC SV0433 Alarm: Inverter DC Link Voltage Low
The FANUC SV0433 alarm indicates an inverter DC link voltage low condition. This alarm occurs when the DC voltage in the main circuit, also known as the DC bus voltage or DC link voltage, drops below the required level. In FANUC servo systems, the servo amplifier or common power supply module depends on stable main circuit input power. If the main power voltage drops, the DC link wiring is loose, the magnetic contactor does not operate correctly, or the emergency stop circuit prevents the main power from being supplied, the... Read more...

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