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 SP9123 Alarm C3: Spindle Switching Circuit Error and Troubleshooting
FANUC SP9123 means that the requested spindle-switching state does not match the internal state of the motor/spindle sensor signal switching circuit. The CNC displays SP9123, while the spindle amplifier displays C3. The affected circuit is the auxiliary module SW, also identified as the submodule SW or SSW. FANUC uses this module in supported spindle-switching configurations where one spindle amplifier controls two spindle motors. The official maintenance procedure identifies the SSW as the primary failed component. On applicable αi-B systems, FANUC also lists the cable between the spindle amplifier and SSW,... Read more...
FANUC SP9120, SP9121, and SP9122: C0/C1/C2 Communication Data Errors
FANUC SP9120, SP9121, and SP9122 mean that an error occurred in the serial communication data exchanged between the CNC and the spindle amplifier. The CNC displays SP9120, SP9121, or SP9122, while the spindle amplifier displays C0, C1, or C2 respectively. FANUC groups all three codes under the same fault description and troubleshooting procedure. The official alarm-list order is to replace the communication cable between the CNC and spindle amplifier, then replace the spindle amplifier control printed-circuit board, and finally replace the CNC main board or sub CPU board associated with... Read more...
FANUC SP9111 Alarm b1: Converter Control Power Supply Low Voltage and Troubleshooting
FANUC SP9111 means that the converter or common power-supply control voltage is too low. The CNC displays SP9111, the spindle amplifier can display b1/B1, and a separate FANUC αi Power Supply normally displays alarm 6. SP9111 is reported through the spindle alarm path, but it does not automatically prove that the spindle amplifier is defective. On an amplifier group with a separate αi Power Supply, FANUC's official procedure directs the technician to check the incoming control power and replace the Power Supply if the alarm occurs as soon as control... Read more...
FANUC SP9110 Alarm b0: Amplifier Communication Error and Troubleshooting
FANUC SP9110 means that communication between amplifiers has failed. The CNC displays SP9110, while the spindle amplifier displays b0 or B0 depending on the display convention. The communication path can include the spindle amplifier, servo amplifier, and power supply. On applicable αi and αi-B systems, the inter-amplifier communication cable is connected through CXA2A and CXA2B. FANUC's official procedure starts with the connector arrangement and communication cable before any amplifier is replaced. Alarm item Display or condition Meaning CNC alarm SP9110 An inter-amplifier communication error was reported Amplifier display b0 /... Read more...
FANUC SP9091 Alarm 91: Pole Position Count Miss and Troubleshooting
FANUC SP9091 means that the spindle amplifier detected an error in the calculated magnetic pole position of a BiS Series synchronous spindle motor. The CNC displays SP9091, while the spindle amplifier displays alarm 91. FANUC describes the fault as a pole position count miss. The alarm is generated when the magnetic pole position detected at the motor sensor's one-rotation signal differs greatly from the value expected from parameter No. 4084, the AMR offset. Alarm item Display or condition Meaning CNC alarm SP9091 / SERIAL SPINDLE ALARM The spindle system reported... Read more...
FANUC SP9089 Alarm 89: Submodule SM (SSM) Error and Troubleshooting
FANUC SP9089 means that the spindle amplifier detected an abnormality involving the submodule SM, also identified as the SSM, used with a BiS Series synchronous spindle motor. The CNC displays SP9089, while the spindle amplifier displays alarm 89. FANUC Maintenance Manual B-65285EN/04 identifies four main possibilities: an incompatible spindle amplifier, an SSM that is not installed or connected, a disconnected JYA4–CX31 interface cable, or a faulty SSM. Alarm location Display Meaning CNC SP9089 An abnormal condition was detected in the SM/SSM submodule system Spindle amplifier 89 The spindle amplifier detected... Read more...
FANUC SP9087 Alarm 87: Spindle Sensor Signal Error and Troubleshooting
FANUC SP9087 means that the spindle amplifier detected an abnormal spindle-sensor feedback signal. The CNC displays SP9087, while the spindle amplifier displays alarm 87. FANUC Maintenance Manual B-65285EN/04 states that alarm 87 must be troubleshot by referring to alarm 83. In that procedure, the spindle amplifier checks the number of phase-A and phase-B feedback pulses each time the one-rotation signal occurs. The alarm is generated when the pulse count falls outside the specified range. SP9087 is therefore not simply a disconnected-sensor alarm; it identifies an abnormal relationship between the A/B... Read more...
FANUC SP9086 Alarm 86: No Spindle Sensor One-Rotation Signal and Troubleshooting
FANUC SP9086 means that the spindle amplifier did not detect the required one-rotation signal from the spindle sensor. The CNC displays SP9086, while the spindle amplifier displays alarm 86. FANUC Maintenance Manual B-65285EN/04 states that no spindle-sensor one-rotation signal occurred and instructs technicians to troubleshoot alarm 86 by referring to the alarm-82 procedure. Alarm 82 covers a missing motor-sensor one-rotation signal; for SP9086, the same diagnostic logic must be applied to the actual spindle-sensor circuit. Alarm item Display or condition Meaning CNC alarm SP9086 Required spindle-sensor one-rotation signal was not... Read more...
FANUC SP9085 Alarm 85: Spindle Sensor One-Rotation Signal Error and Troubleshooting
FANUC SP9085 means that the spindle amplifier detected the spindle sensor's one-rotation signal at an incorrect position. The CNC displays SP9085, while the spindle amplifier displays alarm 85. This wording is important. Alarm 85 does not mean that the one-rotation signal is completely absent. A missing spindle-sensor one-rotation signal is SP9086 / amplifier alarm 86. With SP9085, a signal occurred, but its position was inconsistent with the expected spindle feedback relationship. FANUC Maintenance Manuals B-65285EN/04, B-65515EN/01, and B-65325EN/02 instruct technicians to troubleshoot alarm 85 by referring to the alarm-81 procedure.... Read more...
FANUC SP9082 Alarm 82: Motor Sensor One-Rotation Signal Not Detected
FANUC SP9082 means that the required one-rotation signal from the spindle motor-sensor system was not generated or could not be detected. The CNC displays SP9082, while the spindle amplifier displays alarm 82. FANUC Maintenance Manual B-65285EN/04 defines alarm 82 as: the one-rotation signal of the motor sensor is not generated. Its official troubleshooting sequence is to check the detector parameters, the αiMZ or αiBZ sensor and its connection cable, an external one-rotation input when used, and finally the spindle amplifier. The βiSVSP manual B-65325EN/02 separates the same procedure into an... Read more...
FANUC SP9081 Alarm 81: Motor Sensor One-Rotation Signal Error and Troubleshooting
FANUC SP9081 means that the position at which the spindle motor sensor generates its one-rotation signal is incorrect. The CNC displays SP9081, while the spindle amplifier displays alarm 81. This definition is important because alarm 81 is sometimes described incorrectly as “no one-rotation signal.” FANUC assigns that condition to alarm 82 / SP9082. With SP9081, the drive is receiving or evaluating a one-rotation reference, but its occurrence does not agree with the expected motor-to-spindle relationship. FANUC Maintenance Manual B-65285EN/04 divides the official checks into two configurations: systems using an external... Read more...
FANUC SP9084 Alarm 84: Spindle Sensor Signal Disconnected and Troubleshooting
FANUC SP9084 means that the spindle amplifier detected a disconnected or abnormal spindle-sensor feedback signal. The CNC displays SP9084, while the spindle amplifier displays alarm 84. FANUC Maintenance Manual B-65285EN/04 describes alarm 84 as a disconnected spindle-sensor signal and instructs technicians to use the alarm-73 troubleshooting procedure. This does not make SP9084 identical to SP9073: alarm 73 concerns the motor sensor, while alarm 84 concerns the separate spindle sensor. The diagnostic logic is shared, but the actual detector, feedback channel, connector, and cable must match the installed machine. Alarm item... 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