The FANUC 0i series (0i-A/B/C and 0i-Mate) is one of the most common FANUC control families on shop floors today. Its alarm logic largely follows the classic FANUC structure; however, because the 0i architecture uses the FSSB (serial servo bus) and a serial spindle link, it has alarms of its own, and some system alarm numbers carry different meanings than on the older 0 series. On this page you will find only the alarms and differences specific to 0i / 0i-Mate; for the full map of alarm groups shared by all series, see our main guide: FANUC Alarm Codes and Solutions.
What Is Different on 0i / 0i-Mate? (Summary)
Four things set this series apart. First, the servo drives connect to the control over a fiber-optic FSSB line, so FSSB alarms appear in the 5134–5198 range. Second, the spindle drive communicates over a serial link, making alarms 749/750 specific to this family. Third, the 900–976 system alarms are renumbered (ROM/DRAM/SRAM parity, PMC, NMI, bus errors). Fourth, the 0i keeps a System Alarm History screen: details of system alarms that disappear after a power cycle can still be read there — gold when briefing service.
Alarms Specific to or Different on 0i / 0i-Mate
| Code | Meaning and how to approach it |
|---|---|
| 90 | Reference return completed abnormally. The axis may have started homing from too short a distance, or the encoder one-rotation signal is not being read; move the axis away and retry, and if it repeats have the encoder and cabling checked. |
| 300 | Reference return request: the absolute encoder has lost its position (usually after battery replacement/discharge). Re-reference the axes. |
| 401 / 404 | V-READY off / V-READY unexpectedly on: a break in the servo-ready chain (E-stop, MCC, drive power, FSSB). Proceed exactly as in the servo section of the main guide. |
| 417 | Digital servo system abnormal: an invalid servo parameter value (motor type, direction, pulse settings). Undo the last parameter change; if none was made, verify the servo parameter set with service. |
| 462 / 463 | CNC data send / slave data send failed: data could not reach the drive over the FSSB line. Check the fiber-optic connectors, their latches and the drive power. |
| 700 / 701 | Overheat — 700 control unit, 701 fan motor: clean cabinet fans and filters, verify the fan spins, check the cabinet cooler. One of the most common alarms in summer. |
| 704 | Spindle speed fluctuation detected: RPM deviates under cutting load. Check belt tension, tooling/cutting conditions and the spindle drive. |
| 749 | Serial spindle communication error: the serial link between control and spindle drive dropped. Check the link cable, shielding and drive status; electrical noise is a frequent cause. |
| 750 | Spindle serial link start-up failure: the spindle drive did not become ready at power-up. Check whether the drive powers up and shows an error code; verify the power-up sequence (drive first, then NC). |
| 5134–5198 | The FSSB alarm family — 5134 open-ready timeout, 5135 error mode, 5136 number of amplifiers too small (one drive is not seen), 5137 configuration error, 5197 open timeout, 5198 ID data not read. Common approach: check the fiber-optic FSSB cable, drive power supplies and the axis–amplifier assignment parameters. With 5136, one drive is most likely not receiving power. |
| 926 | FSSB bus alarm (system level): a serious communication fault on the line. If it survives a power cycle, the fiber line and drive boards need service attention. |
0i System Alarms (900–976): Renumbered vs the Old 0 Series
| Code | Meaning on the 0i series |
|---|---|
| 900 | ROM parity error. |
| 912–919 | DRAM parity errors. |
| 920 | Servo alarm / watchdog (broader than on the 0 series — covers servo-side system faults, not only the main board). |
| 930 | CPU interrupt alarm. |
| 935 | SRAM ECC error — a bad memory cell; this is exactly why your program/parameter backup must be current. |
| 950 / 951 | PMC system alarm / PMC watchdog alarm. Careful: on the old 0 series, 950 is a +24V fuse failure — do not mix the series up. |
| 972 / 973 | NMI alarms: 972 on an option board (present on 0i-B and 0i-C, not on 0i-Mate), 973 of unknown cause. |
| 974–976 | F-BUS / bus / local bus errors — board-level communication faults, a service matter. |
Use the System Alarm History Screen
The 0i’s greatest gift to the operator is that alongside the standard alarm history it keeps a system alarm history: even when a system alarm such as 930 disappears from the screen after a power cycle, its details (which board, which address) remain readable there. Opening that screen and noting the details before calling service shortens downtime considerably. For the screens themselves, see FANUC Alarm, Message and Diagnosis Screens. P/S (program) alarms are shared across series — see the P/S Alarm Codes list, and for the parameter side our Comprehensive FANUC Parameter Guide.
Frequently Asked Questions
How do I tell whether my machine is 0i or 0i-Mate?
The series name is shown on the boot screen and the SYSTEM screen (e.g. Series 0i-MC, 0i Mate-TC). The 0i-Mate is the economy version of the 0i with fewer axes and options; the alarm structure is the same.
I get FSSB alarm 5136 and the machine will not start — where do I begin?
5136 usually means one of the drives is not receiving power. In order: are the LEDs on each drive lit, are the drive fuses/power feeds intact, and is the fiber-optic FSSB cable clicked firmly home at both ends? These three checks resolve the majority of cases.
Why does alarm 90 (REFERENCE RETURN ABNORMAL) appear on a FANUC 0i, and how do I clear it?
The axis did not approach the reference point fast enough or from far enough away, so the one-revolution signal could not be read reliably. Try in this order:
- Move the axis away from the reference point by more than one motor revolution (a few centimetres in machine coordinates is enough).
- Do not leave rapid override at F0 or 25 %; during the approach the position error in DGN 300 must exceed 128.
- Select REF/ZRN mode and hold the axis key until the return completes.
- If it still appears, compare parameters 1420 (rapid rate), 1425 (FL rate) and 1825 (servo loop gain) with the builder’s list; after that the encoder supply (above 4.75 V) and cable are a service job.
How do I clear alarm 300 (REFERENCE RETURN REQUEST)?
The absolute encoder has lost its position data (flat battery, encoder cable unplugged, encoder replaced). The fix is a new reference return:
- If a battery warning is present, replace the battery first.
- Select REF/ZRN mode and reference only the axis that raised the alarm.
- If the alarm itself blocks the reference return, bit 5 (APC) of parameter 1815 is temporarily set to 0, the return is performed, and the bit is set back to 1. This needs parameter write enable (PWE); take a backup first.
- If the encoder was replaced, the reference position may differ from before; it is corrected with 1850 (grid shift), which is service work.
What should I check first on alarm 401 (V READY OFF)?
The servo amplifier is not giving, or has dropped, its ready signal. Most of the time the surroundings are at fault, not the drive:
- Is emergency stop pressed, or is the E-stop chain (door, panel switch) open?
- Does the PSM (power supply module) have control power, is the breaker on?
- Is the MCC (main contactor) pulled in, and if there is an external MCC sequence, is that satisfied?
- Is an alarm code shown on the PSM or SPM? Clear that first; 401 is often the consequence of another servo alarm.
- Is the terminating connector fitted to JX1B on the last drive?
If all of these are fine, the drive or the axis control card in the CNC is faulty and service is needed.
Which parameters does alarm 417 (DIGITAL SERVO PARAMETER INCORRECT) refer to?
The cause is shown bit by bit in DGN 203. Parameters to check: 2020 (motor type), 2022 (rotation direction, must be 111 or -111), 2023 (velocity feedback pulses), 2024 (position feedback pulses), 1023 (servo axis number, must be consecutive), 2084/2085 (flexible feed gear). Undo the last parameter change; if there was none, set 2047 to 0 and repeat the servo parameter initial setting. That resets the servo settings and should be done by service.
What should I do on overheat alarms 700 and 701?
700: the ambient temperature of the control unit has exceeded 55 °C. Leaving the cabinet door open is not a fix; clean the cabinet fan and filters, check the cabinet air conditioner if fitted, and look for a heat source blowing into the cabinet (drive fan, transformer). 701: the fan motor on top of the cabinet has stopped or overheated; check it and replace if needed. If 700 recurs with a normal ambient temperature, the temperature circuit on the main board may be faulty.
Why does alarm 704 (spindle speed fluctuation) appear?
The speed has deviated from the commanded value under load. First check whether the cut is heavy and whether the tool is worn; watch the spindle load meter. Check belt tension. If those are normal, parameters 4911–4914 (fluctuation detection ratio and time) are compared with the builder’s values; the spindle drive or motor is the last suspect.
How do I tell serial spindle alarms 749 and 750 apart?
749 is a loss of communication during operation: check the JA7A–JA7B cable between the CNC and the spindle drive (SPM), make sure the connectors are seated and the cable is routed away from power cables; noise is a common cause. 750 is the drive not being ready at power-on: if the drive LED shows anything other than “24”, clear that alarm first, then switch the drive and CNC off and on together. Detail is shown in DGN 409: SHE = serial circuit in the CNC, S1E/S2E = first or second spindle, SPE = parameter mismatch.
What is a practical check order for alarm 5136 (FSSB: NUMBER OF AMPS IS SMALL)?
The CNC sees fewer drives than axes. The FSSB setting screen lists only the recognised drives; look at the first drive that is missing:
- Does that drive have power and a lit LED?
- Unplug and re-click the fibre-optic cable between the last recognised drive and the first missing one at both ends.
- A +5 V line shorted to ground in a pulse coder cable pulls the drive supply down and triggers this alarm; check the cable for damage.
- If all is well, the drive or the axis control card in the CNC is faulty.
Are programs and parameters lost when alarm 935 (SRAM ECC ERROR) appears?
Not necessarily. Two or more bits of a data word in SRAM have been corrupted. Check the battery first: when the 3 V battery drops to 2.6 V, BAT flashes on the screen; replace it immediately. Then, if an SRAM backup exists, restore it from the BOOT screen; if not, an all-clear is performed and parameters, PMC parameters and programs are re-entered by hand. If the alarm recurs, the FROM/SRAM module must be replaced. This alarm is the most concrete reason to take regular SRAM backups.
Which parameters do RS-232 alarms 85, 86 and 87 point to?
85: baud rate or communication settings do not match. 86: the device is not ready, no cable or no device power. 87: the transfer is corrupted. On the CNC side, 0020 (I/O channel) and, for that channel, 0101/0111/0121 (stop bits, code), 0102/0112/0122 (device type, 0 for RS-232) and 0103/0113/0123 (baud: 10 = 4800, 11 = 9600, 12 = 19200) must match the PC settings. A wrong PUNCH CODE (0 EIA, 1 ISO) on the SETTING screen gives 86. The cable leaves the JD5A/JD5B connector; the pin-out is in our RS-232 cable guide.
The machine does not move but shows no alarm. Where do I look?
At the status line at the bottom of the screen: EMG (emergency stop), RESET, or no mode name (JOG/HND/MDI/MEM) is the first clue. Then look for the line showing 1 in diagnostic DGN 000–015: 005 interlock, 004/013 override 0 %, 003 waiting for in-position, 000 waiting for the M code finish signal. The step-by-step version of this diagnosis is in our “FANUC machine does not move” guide.
Other series guides: If your machine runs a 21i/21i-TB or 18i control, see our FANUC 21i / 21i-TB Alarms page.
On the operator side: For what to do about each cycle, overtravel, servo, spindle and battery alarm an operator actually meets, see our FANUC Operator Alarms page. If the alarm comes from a programming error, the FANUC G and M Code List also helps.