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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 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...
FANUC SV0432 Alarm: Inverter Control Voltage Low
The FANUC SV0432 alarm indicates an inverter control voltage low condition. This alarm occurs when the control voltage of the servo amplifier or common power supply drops below the required level. In many cases, SV0432 is related to a voltage drop in the servo amplifier system, the common power supply input module, or the internal control power supply circuit. It may also be caused by poor connection between servo amplifiers, insufficient input voltage, abnormal 24V control power, insufficient power supply capacity, external wiring problems, or a faulty common power supply... Read more...
FANUC SV431 Alarm: Inverter Circuit Normal
The FANUC SV431 alarm is related to the inverter circuit normal signal. This alarm may occur when the CNC system detects an abnormal condition related to the servo amplifier, common power supply, or related alarm signal circuit. In many cases, SV431 is associated with servo amplifier overheating or common power supply overheating. It may also be related to incorrect amplifier wiring, incorrect ALM signal handling, analog servo adapter wiring issues, incorrect motor parameters, or servo amplifier failure. Because this alarm can involve both signal wiring and actual servo hardware condition,... Read more...
FANUC SV0430 Alarm: Servo Motor Overheat
The FANUC SV0430 alarm indicates a servo motor overheat condition. This alarm occurs when the temperature detection element inside the encoder detects that the servo motor temperature is too high. When SV0430 appears, the problem may be caused by actual servo motor overheating, incorrect servo motor parameters, abnormal temperature detection hardware, encoder failure, feedback cable problems, amplifier issues, brake problems, cooling problems, excessive mechanical load, or unsuitable machining conditions. For troubleshooting, the CNC diagnosis screen is very important. Diagnosis No.308 shows the servo motor temperature, and diagnosis No.309 shows the... Read more...
FANUC SV0423 Alarm: Excessive Error in Torque Control
The FANUC SV0423 alarm indicates an excessive error in torque control. This alarm occurs when the accumulated movement value in torque control exceeds the allowable value set by parameter. In torque control mode, the CNC system monitors not only the torque command but also the movement accumulation allowed during torque control. If the accumulated movement becomes larger than the permitted threshold, the system may generate the SV0423 alarm. This alarm is usually related to the torque control movement accumulation parameter, torque control program logic, actual mechanical condition, or an unsuitable... Read more...
FANUC SV0422 Alarm: Torque Control Overspeed
The FANUC SV0422 alarm indicates a torque control overspeed condition. This alarm occurs when the allowable speed specified in torque control has been exceeded. In torque control mode, the CNC system controls the servo axis according to a torque command while also monitoring the allowed speed limit. If the actual or commanded operating condition exceeds the specified allowable speed in torque control, the system may generate the SV0422 alarm. This alarm is mainly related to the torque control command, torque setting value, speed limit value, torque control parameters, and the... Read more...

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