The Fanuc 16i / 18i / 21i-Model B controllers are the B-generation update of the popular 16i/18i/21i family. They use the same plain numeric alarm format as the A models. Here are the alarms seen most often, with causes and fixes.
How 16i/18i/21i-B Alarm Numbers Map
- 000–199 — Program / parameter • 300s — APC (encoder)
- 400s — Servo • 500s — Overtravel • 700s — Overheat / spindle • 900+ — System / watchdog
Common 16i/18i/21i-B Alarms
| Alarm | Meaning | Common Cause & Fix |
|---|---|---|
| 000 | Please turn off power | Power-cycle after a parameter change. |
| 100 | Parameter write enable | Set PWE = 0 and press RESET. |
| 300 | APC alarm — reference return required | ABS position lost (battery change). Perform zero-return. |
| 401 | Servo amplifier VRDY OFF | Amp not ready — check DC link, E-stop, amp power and fault LED; repair/replace drive. |
| 404 | VRDY signal ON (stuck) | Faulty servo amplifier or wiring. |
| 410 / 411 | Excessive position error (stop / move) | Bind, overload, encoder or amplifier/motor fault. |
| 414 | Digital servo system fault | Check the amplifier alarm code, motor and feedback. |
| 417 | Illegal digital servo parameter | Restore parameters; replace CNC battery A98L-0031-0025. |
| 500 / 501 | Stored stroke limit + / − exceeded | Jog back inside range and reset. |
| 700 | Overheat: control unit | Check cabinet cooling fan and ambient temperature. |
| 704 | Spindle speed fluctuation / overheat | Overload, belt slip, motor or spindle amplifier fault. |
| 900 / 910 / 930 | System / RAM / CPU (watchdog) alarm | Re-seat boards; a faulty main/CPU board may need repair or replacement. |
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Quick-reference of common alarms. For the complete list, refer to the Fanuc 16i/18i/21i-B Maintenance Manual.