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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 SV0409 Alarm: Checked Torque Abnormal
The FANUC SV0409 alarm indicates a checked torque abnormal condition. This alarm occurs when the CNC system detects an abnormal load after the abnormal torque load detection function has been enabled. In simple terms, the control system has detected that the load on a servo motor, Cs axis, or spindle positioning axis is outside the expected range. This may be caused by an actual mechanical overload, incorrect servo-related settings, abnormal machining conditions, or a fault in the servo motor or servo drive. What Does FANUC SV0409 Alarm Mean? SV0409: Checked... Read more...
FANUC SV404 Alarm: Servo Ready Signal VRDY Stays ON
The FANUC SV404 alarm is related to the servo ready signal of the servo amplifier. This alarm occurs when the servo amplifier's VRDY signal, also known as the servo ready signal, remains ON continuously when the CNC system detects an abnormal servo ready status. In normal operation, the CNC system checks the ready status of the servo amplifier before enabling servo control. If the VRDY signal stays ON abnormally, the system may judge that the servo ready circuit, amplifier, or axis control hardware is not operating correctly, and the SV404... Read more...
FANUC SV0403 Alarm: Hardware/Software Mismatch on Servo Axis Card
The FANUC SV0403 alarm usually indicates a hardware/software mismatch in the servo control system. This alarm is commonly related to an incorrect combination between the axis control card and the servo software installed in the CNC system. When this alarm appears, it means the CNC system has detected that the servo-related hardware and software are not correctly matched. In most cases, this is not a simple parameter setting issue. It is usually related to the installed axis card, servo software, or system configuration. What Does FANUC SV0403 Alarm Mean? SV0403:... Read more...
FANUC SV0436 Soft Thermal Relay OVC Alarm: Causes and Troubleshooting Guide
FANUC SV0436, also displayed as SV436 on some CNC systems, is a soft thermal relay alarm related to OVC protection. It means the digital servo software has calculated that the servo motor is operating under excessive load for too long. This alarm is designed to protect the motor and servo system before damage occurs. What Is FANUC SV0436 Alarm? FANUC SV0436 Soft Thermal Relay OVC alarm indicates that the CNC servo software has detected a calculated thermal overload condition. It does not always mean that the servo motor is physically... Read more...
FANUC IE Alarm List: Misoperation Prevention Alarms
This page covers FANUC IE alarms related to the misoperation prevention function, including soft limit detection, excessive commanded rotation speed, illegal acceleration or deceleration, and abnormal machine coordinate position conditions. These alarms are important because they are generated by a preventive protection function designed to detect unsafe or invalid motion conditions before machine damage or incorrect operation can occur. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical maintenance and machine operation, IE alarms are closely related to motion safety logic, stored... Read more...
FANUC DS Alarm Codes: External Data, Verify and System Protection Alarms
This page covers FANUC DS alarms related to external data input/output, program and workpiece search, external operator information display, address and data signal errors, verification mismatches, and system protection functions. These alarms are important because they are tied to data exchange, machine-side interface logic, program handling, and integrity checking of CNC-related software and parameters. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical service work, this group of DS alarms often appears when external data interfaces are used, when search conditions are... Read more...
FANUC DS Alarm Codes: Synchronization, APC, Reference Return and DCS Errors
This page covers FANUC DS alarms related to synchronization control, APC conditions, reference return, DCS-related settings, detector reference mark logic, PMC axis control, and servo motor spindle setup. These alarms are important because they often affect the machine’s ability to maintain axis coordination, establish reference position correctly, or recover normal position-related operation after power-on or maintenance work. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical maintenance work, this group of DS alarms often appears when synchronization settings are inconsistent, APC battery... Read more...
FANUC OH Alarm List: Overheat and Cooling Fan Alarms
This page covers FANUC OH alarms related to controller overheating, PCB cooling fan failure, and spindle overheat conditions. These alarms are important because they point to thermal protection conditions that can affect CNC stability, electronic component life, and safe machine operation. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical maintenance work, OH alarms often appear when the CNC cabinet temperature rises too high, when the cooling fan for the control PCB fails, or when spindle heat is judged to be abnormal... Read more...
FANUC SP Alarm Codes: Serial Spindle Communication and Control Errors
This page covers FANUC SP alarms related to serial spindle communication, spindle control faults, spindle amplifier errors, spindle-side initialization problems, and spindle parameter setting failures. These alarms are especially important in service and repair work because they often point to communication instability between the CNC and spindle amplifier, spindle control hardware problems, incorrect spindle parameter allocation, or failure in spindle-side initialization. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical maintenance work, this group of spindle alarms is often more serious than... Read more...
FANUC SP Alarm Codes: Rigid Tapping, Spindle Position and Deviation Alarms
This page covers FANUC SP alarms related to rigid tapping, spindle mode switching, spindle positioning, spindle deviation, spindle load detection, position coder conditions, spindle gear ratio settings, and communication data abnormalities. These alarms are especially relevant in applications where spindle positioning accuracy, spindle synchronization, and rigid tapping performance directly affect machining quality. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical maintenance work, this group of SP alarms is commonly associated with spindle positioning errors, excessive spindle deviation, incorrect spindle selection, encoder-related... Read more...
FANUC IO and PW Alarm Codes: File System, Memory and Power-Off Required Alarms
This page covers FANUC IO alarms related to file systems, memory access, and program storage, as well as PW alarms related to power-off required conditions, parameter setting faults, and PMC address assignment errors. These alarm groups are important because they are connected to CNC data handling, parameter integrity, control configuration, and machine restart requirements. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical service work, IO alarms often point to problems involving the CNC file system, program storage memory, or tool data... Read more...
FANUC OT Alarm List: Overtravel and Limit Alarms
This page covers FANUC OT alarms related to overtravel conditions, soft limits, hard limits, interference detection, and travel pre-check errors. These alarms are commonly generated when an axis moves beyond an allowed machine travel range, enters a prohibited zone, reaches a hardware limit switch, or is judged in advance to exceed the allowable travel area. These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D. In practical machine maintenance and operation, OT alarms are among the most familiar CNC alarms because they are directly related... Read more...

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