Error Code: Fanuc Alarm 414
What it means: Alarm 414 (SERVO ALARM: n-TH AX — EXCESS ERROR) is a following error fault. In servo control, “following error” is the difference between where the CNC control commands the axis to be and where the encoder reports it actually is. When this error exceeds the tolerance set in the Fanuc parameters, the control triggers Alarm 414 and halts all motion.
Following error is always present during motion (it’s physically impossible to have zero lag). The alarm means the lag became large enough that the control concluded something was wrong — either the axis couldn’t keep up with the commanded motion, or the encoder is reporting a position that doesn’t match reality.
Common Causes
- Mechanical binding or excessive load — The motor can’t drive the axis fast enough to keep up with the commanded position, causing following error to grow until the alarm trips. Ballscrew damage, way contamination, or a crash that bent components are common culprits.
- Servo gain too low (position loop gain — parameter 1825) — A low gain setting allows large following errors under normal loads. The control doesn’t respond aggressively enough to position error.
- Following error tolerance too tight (parameter 1828) — If someone set an unusually tight tolerance for the application, normal following error during acceleration phases can trip the alarm.
- Encoder signal problem — A damaged encoder cable causing intermittent signal loss produces random, large following errors. The motor is moving, but the encoder tells the control it’s somewhere else.
- Motor coupling or ballscrew coupling slippage — If the coupling between the motor shaft and the ballscrew slips, the motor spins but the axis doesn’t move. The following error grows until alarm.
- Servo amplifier fault — A failing amplifier may not deliver the commanded current, causing the motor to fall behind under load.
Step-by-Step Fix
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Determine when the alarm triggers. Does it happen at startup (before movement), during rapid traverse, during feed moves, or only during heavy cuts? Startup = encoder or parameter issue. During rapids = tolerance or gain issue. During heavy cuts = mechanical overload.
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Check for mechanical binding. E-stop the machine and carefully hand-push or jog the axis at very low speed. Smooth = no mechanical issue. Rough, grinding, or points of high resistance = mechanical problem. Inspect way lube, check ballscrew for damage, look for crash debris in the ways.
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Check the motor coupling. On belt-drive or direct-couple designs, physically grip the motor shaft coupling and the ballscrew coupling separately. Try to rotate them relative to each other — any movement between them indicates a failed set screw or damaged coupling. Replace the coupling and re-torque set screws.
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Inspect encoder cable routing. Trace the encoder cable from the motor to the servo amplifier. Look for: pinched sections at way cover edges, cables draped over moving components, damaged outer shielding, or connectors that are loose at either end. A cable that flexes with every axis move and has a nick will produce intermittent following errors.
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Check the following error tolerance parameter. On the Fanuc control, navigate to Parameters → Servo Parameters and find parameter 1828 (in-position width) and the following error limit (parameter 1828 or 2068 depending on the Fanuc series). Compare against Fanuc’s default values for your motor/amplifier combination. If the tolerance is set dramatically below the default, it may have been set for a specific precision application and is now causing nuisance alarms due to mechanical wear.
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Monitor following error in real time. Use the Fanuc servo diagnostic screen (DGNOS or the servo axis diagnostic page) to watch the following error value in real time during a move. On a healthy axis, following error should track proportionally with speed and return to near-zero when stopped. A following error that spikes randomly (not related to speed) during motion points to encoder issues.
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Check servo load meter during the fault conditions. If following error alarms only during heavy cuts, the axis is being mechanically overloaded. Reduce depth of cut, feedrate, or increase the following error tolerance for that application.
Parts That May Need Replacement
| Part | Where to Buy | Typical Cost |
|---|---|---|
| Encoder cable (Fanuc encoder cable, model-specific) | Fanuc America, Motion Controls LLC | $80–$350 |
| Motor coupling (Lovejoy or Ruland, size-matched) | MSC Industrial, McMaster-Carr | $30–$120 |
| Absolute encoder / pulse coder (A860-0309 series) | Fanuc America, CNC dealers | $400–$1,200 |
| Ballscrew (machine-specific) | NSK, THK distributors | $500–$3,000 |
When to Call a Professional
If mechanical checks are clean, the coupling is solid, encoder cable looks good, and you’re still getting Alarm 414 — you need servo parameter analysis by a Fanuc-certified technician. Following error alarms that can’t be traced to mechanical or cable issues usually point to servo gain tuning problems or a failing servo amplifier that’s not delivering commanded current accurately. These require live servo oscilloscope traces and parameter adjustment under controlled conditions. Tell the tech: “Alarm 414 on axis [n], no mechanical binding, coupling is tight, encoder cable is intact. I need servo gain analysis and amplifier output verification.”
Pro tip: On Fanuc Series 0i and 16i/18i systems, you can read the actual following error value in real time from the diagnostic data screen (diagnostic numbers 300-305, one per axis). A following error that’s consistently 100–200 units at low speed but suddenly spikes to 10,000+ units without a corresponding speed change is almost always an encoder cable fault — the pulse stream drops out briefly and the reported position jumps.