FANUC Alarm Codes: The Ones You'll Actually See

Start With the Symptom, Not the Code

Most people looking up a FANUC alarm do not actually know the code. They know the machine stopped, and roughly what it was doing when it did.

How to Read a FANUC Alarm Number

A FANUC alarm code is a two-letter prefix followed by digits: SV401, PS010, SP749. The prefix names the subsystem that owns the fault. The digits only identify which fault inside that subsystem.

SV0410 is a servo-side problem: a drive technician with an oscilloscope. PS0090 is an operator-side problem: somebody needs to send the machine home. Same digits, two different people, two different rooms. Knowing which one you are holding before you know what is broken tells you who to call.

The prefixes you will meet

PW, IE, ER and 9xx are here because you will see them on your screen, not because we can explain them. A wrong row is worse than a missing one.

The 7nxx spindle rule

In a FANUC 7nxx spindle alarm, n is the spindle number. The first spindle displays 7001, the second 7101. So 7n12 is one alarm on spindle one and a different alarm on spindle two. Confirm which spindle the control names before you order an amplifier.

Same number, different generation

Alarm numbers overlap across 0i-D, 0i-F, 0i-F Plus and 30i-B while the meanings shift. FANUC's current CNC control series shows which of those are still shipping.

The 400 block and the SVxxxx block are two different numbering systems. SV0410 and SV0361 do not belong to the same sequence, and the same digits do not mean the same thing in both. Match prefix, number and your own control's manual before you act.

The Codes, by What the Machine Is Doing

Seven groups. Each group shares a troubleshooting order, so the group tells you more than the individual code does.

Every entry below comes from a check against two independent sources. Where those sources disagree, the code is not listed at all — DS306 is the one that had to go, because one set of sources describes it as a battery warning and another as a zero-voltage alarm that loses the reference position. Where the English screen text could not be confirmed, the entry says so instead of paraphrasing one.

If you are writing up a code that is not here, link to the group rather than the page.

Nothing will move: SV401, SV400, SV404, SV431, SV432, SV607

SV401 — SERVO ALARM: n-TH AXIS VRDY OFF. The servo amplifier's ready signal is off. Check the E-stop circuit, the amplifier supply and LEDs, and the DC link. The E-stop circuit is a safety function in its own right, covered by ISO 13850.

SV400 — SERVO ALARM: n-TH AXIS OVERLOAD. The overload signal for axis n is on. Check diagnostics 201 and 720–721, reduce the load, and check brake release and lubrication.

SV404 — SERVO ALARM: n-TH AXIS VRDY ON. The ready signal is still on after MCON drops. Check the connection between the amplifier and the interface module.

SV431 — n AXIS: CNV. OVERLOAD. The power module or β-series SVU is over temperature. Improve cabinet cooling and check the fans.

SV432 — n AXIS: CNV. LOWVOLT CON. The converter's control supply voltage has dropped. Check the 200 V input and the control supply.

SV607 — n AXIS: CNV. SINGLE PHASE FAILURE. Input voltage is missing a phase. Check the three-phase supply and the breaker.

Position error: SV410, SV411, SV413, SV414, SV417, SV0361

SV410 — SERVO ALARM: n-TH AXIS EXCESS ERROR. Position error above the set value while the axis was stopped. Check the gain, the encoder and mechanical binding.

SV411 — SERVO ALARM: n-TH AXIS EXCESS ERROR. Position error above the set value while the axis was moving. Check load, gain, speed and encoder.

SV413 — SERVO ALARM: n-TH AXIS LSI OVERFLOW. The error register overflowed past 2^31. Usually a parameter setting rather than a hardware fault: check the servo parameters.

SV414 — SERVO ALARM: n-TH AXIS DETECTION ERROR. The digital servo system reported an abnormality. Check diagnostics 200 and 204, and the amplifier LEDs.

SV417 — SERVO ALARM: n-TH AXIS PARAMETER SETTING ERROR. A servo motor or encoder that this system does not use has been set. Check the motor and encoder model against the parameters.

SV0361 — PULSECODER PHASE ERROR (BUILT-IN). Phase error on the built-in encoder. Check the encoder and the feedback cable.

Feedback path: SV416, SV445, SV446, SV448, SV453, SV0365

SV416 — SERVO ALARM: n-TH AXIS DISCONNECTION. The pulse coder position detection circuit is broken. Check the feedback cable and connectors.

SV445 — SERVO ALARM: n-TH AXIS SOFT DISCONNECTION. Encoder feedback soft disconnection. Check the feedback cable, connectors and shielding.

SV446 — SERVO ALARM: n-TH AXIS HARD DISCONNECT. Encoder feedback hard disconnection. Check the cable for a break, then the encoder itself.

SV448 — SERVO ALARM: FEEDBACK MISMATCH. The two feedback signals do not match. Check both feedback paths and the related parameters.

SV453 — SERVO ALARM: SOFT DISCONNECTION. α pulse coder soft disconnection. Check the encoder cable.

SV0365 — LED ERROR (BUILT-IN). Built-in encoder LED error. Replace the encoder.

Heat: SV430, SV436, SV601, SV602, SV606, OH701

SV430 — n AXIS: SV. MOTOR OVERHEAT. The servo motor is over temperature. Check cooling, load and the continuous rating conditions.

SV436 — n AXIS: SOFTTHERMAL (OVC). Software thermal protection tripped, equivalent to overcurrent. Reduce the load, check cooling and check for mechanical binding.

SV601 — n AXIS: INV. RADIATOR FAN FAILURE. The inverter heatsink cooling fan has failed. Replace the fan.

SV602 — n AXIS: INV. OVERHEAT. The servo amplifier is over temperature. Clear the dust and check the cabinet temperature.

SV606 — n AXIS: CNV. RADIATOR FAN FAILURE. The power module heatsink fan has failed. Replace the fan.

OH701 — no verified screen text. The cooling fan inside the control unit has stopped. Replace the fan.

Spindle: SP749, SP750, 7n01, 7n12, 7n24, 7n27

SP749 — S-SPINDLE LSI ERROR. Serial spindle communication error, covering the fibre optic, the main board and the spindle module. Check the fibre connectors, clean the end faces, and check the module.

SP750 — no verified screen text. Spindle serial link error: the amplifier is not powered, or its ROM version is wrong. Check the amplifier supply and version.

7n01 — SPN_n_: MOTOR OVERHEAT. Spindle motor internal temperature above the limit. Check the ambient temperature and the load; replace the fan immediately if it is not turning.

7n12 — SPN_n_: POWER CIRCUIT OVERCURRENT. Amplifier output current too high. Check motor insulation and spindle parameters, and replace the SVPM if necessary.

7n24 — SPN_n_: SERIAL DATA TRANSFER ERROR. Data error between CNC and spindle, or a broken cable. Route the cable away from power lines and replace it if necessary.

7n27 — SPN_n_: POSITION CODER NOT CONNECTED. Spindle position coder (JYA3) signal abnormal. Replace the cable.

One spindle code sits outside this group: alarm 21, which shows as SP9021 on αi-B drives.

Limits and battery: OT500, OT501, OT506, OT507, DS300, DS307

OT500 / OT501 — OVER TRAVEL: +n / OVER TRAVEL: -n. Positive or negative soft limit I exceeded, parameters 1320 and 1321. Jog the axis back out of the limit.

OT506 / OT507 — OVER TRAVEL: +n / OVER TRAVEL: -n. The positive or negative hard limit switch was reached. Hold the overtravel release and jog back out.

DS300 — no verified screen text. Absolute encoder position lost; a reference return is needed. Replace the battery, then set the reference position again.

DS307 — no verified screen text. Encoder battery voltage low; the APC characters flash in reverse video. Replace the battery within one to two weeks.

Program alarms: PS000, PS010, PS090, PS100, PS101

PS000 — PLEASE TURN OFF POWER. A parameter that only takes effect after a restart was changed. Power the control off and back on.

PS010 — IMPROPER G-CODE. A G-code this system does not support, or has not been optioned for. Check the machine's G-code list and its options.

PS090 — REFERENCE POSITION RETURN INCOMPLETE. Reference return was not completed. Run a manual reference return, then run the program.

PS100 — PARAMETER WRITE ENABLE. The parameter write switch (PWE) is set to 1. Set it back to 0 and press RESET.

PS101 — PLEASE CLEAR MEMORY. A parameter that requires a memory clear was changed. Back up the parameters, then power on with RESET and DELETE held.

Five-Step Triage

Order matters. A part ordered before the checks is a part ordered on a guess.

1. Record the whole alarm, not just the number. Four things: prefix, number, alarm text, and the axis or spindle name. 401 alone is useless. SV401, Z axis, at power-on is a diagnosis already half made.
2. Read the amplifier LEDs and compare. The screen reports the NC side's conclusion; the amplifier LED reports the first-hand condition. When the two disagree, believe the LED. Then read that LED against your amplifier's nameplate model, because the same digit means different things on α, αi and βi.
3. Turn symptoms into numbers. Four diagnostic numbers do most of the work: 200 and 204 for system state, 201 for load and current, 720–723 for the detail behind an overload, 202 for absolute encoder battery voltage. A number separates "the axis feels heavy" from "the axis is at 143% load".
4. Rule out the outside before you open the cabinet. E-stop circuit, three-phase input, 24 V supply, fibre optic connectors, encoder cables, cabinet temperature. None of them require disassembly.
5. Back up parameters before you swap anything. SRAM and parameter backup, on a card you keep. Swapping a board, an encoder or a battery routinely forces a re-initialisation or a reference return, and without a backup a twenty-minute job becomes a commissioning project.

When not to press RESET

A code that comes straight back is telling you the fault is still live. That is useful information. But three situations make RESET the wrong move:

• Before the code is written down. The alarm history holds the recent events, and clearing them loses the pattern that separates an intermittent fault from a repeatable one.
• After a crash, before the axis position is recorded. Once the machine has moved, you cannot reconstruct where it was.
• On an SV or SP alarm you have not diagnosed. A clean screen for ten minutes costs you the only free clue you had.

Repair, Replace, or Send It Out?

By this point you know what failed. The remaining question is commercial, and it deserves a rule rather than a feeling.

Repair wins when the failure is a single point: a fan, an IPM, a power module, a capacitor, an offset circuit. It also wins when the model still has repair parts available, and when the part price is more than three times the repair price.

Replacement wins on board-level, multi-layer faults, and on anything already repaired twice. The 7nxx control-board group is the clearest case: 7n13, 7n32, 7n74, 7n75, 7n79, 7n97, 7n98 are all SVPM control board faults, and the manual's answer for each is to replace the board.

The arithmetic fits on a phone: downtime cost per hour × days waiting, against the premium on a used unit. If the premium is smaller, buy the part.

What "tested" should mean before you install a used part

A used amplifier with a sticker on it is not a tested amplifier. Before it goes in your cabinet it should have been powered up through its own self-test, run under load rather than idled, checked for encoder communication on a live feedback path, watched for temperature rise over a run long enough to expose a marginal heatsink, cleared of its previous alarm history, and verified for firmware version against your control.

We repair, bench-test, and sell new and tested used FANUC parts. Every used unit we ship carries 12 months. That warranty only means anything if the unit earned it: a bench-tested part comes with a load test behind it, and the twelve months is what we are willing to put behind that test. → New and tested used FANUC parts

Preventing the Repeat Alarm

Batteries. Replace the encoder battery with the control powered on. Put the change date on a label inside the cabinet door.

Fans and filters. Clean the filter mats on a schedule, not when someone complains. A fan that has stopped is not a warning; it is a countdown.

Input power. Missing phases, voltage sag and worn contactors. Measure the three-phase supply under load, not at idle, because a marginal phase passes at idle. NFPA 79 requirements for industrial machinery covers the supply-side expectations.

Cables and connectors. Drag chain bend radius, fibre optic minimum bend radius, connector protection in an oil-mist environment, and shield grounding. These four are where an intermittent feedback fault usually starts.

FANUC Alarm Codes FAQ

How do I clear a FANUC alarm?

Clearing a FANUC alarm depends on which prefix you are looking at. PS and OT alarms usually clear with RESET once the cause is corrected. SV, SP and DS alarms will not, because the control keeps re-detecting the fault until the source is removed.

What is the most common FANUC alarm?

There is no published frequency table, so this is workshop experience rather than data: SV401 (VRDY OFF) and SV400 (OVERLOAD) are the two that come up most. SV401 appears at power-on during the ready sequence; SV400 appears on the load side, while the axis is working.

What's the difference between SV and SP alarms?

An SV alarm belongs to the servo system, which drives the feed axes, while an SP alarm belongs to the spindle, which handles rotation and orientation. Both use serial communication, but the fault domains do not overlap: SV owns position, SP owns speed.

What does the "n" mean in a 7nxx spindle alarm?

In a FANUC 7nxx alarm, n is the spindle number. The first spindle displays 7001, the second 7101, so 7n12 is a different alarm on each. Confirm which spindle the control names before you look anything up.

What does DS307 mean, and how long do I have?

DS307 is the absolute-encoder battery warning, and you have roughly one to two weeks. Replace the battery with the control powered on.

Where do I find the alarm history on a FANUC?

Under SYSTEM, then ALARM, then HISTORY, or by pressing the ALARM key and paging through. The history matters more than the current alarm: it shows whether the fault is intermittent or always at the same point in the cycle.

Is a FANUC alarm number the same on 0i and 30i?

Mostly for the 400 and 500 blocks, but not reliably across the board. The 400 block and the SVxxxx block use entirely different numbering. Match prefix, number and your own control's manual, never the number alone.

Still Down? Send Us the Code.

Three things, and we can usually tell you what to check next:

1. The alarm code exactly as it appears on screen: prefix, digits, axis or spindle name.
2. The amplifier or motor part number from the nameplate.
3. Whether it is one axis or all axes.

That is enough to say something useful instead of something general. If it turns out to be a part, we can quote new or tested used. If it is a board, we will tell you whether it is worth repairing.

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