What causes FANUC alarm 427?

Servo amplifier internal fault — check amplifier fault LED and DGN 200 sub-code. Axis encoder cable damaged or connector loose causing position feedback loss. Servo motor winding fault or bearing failure. FSSB communication fault between CNC and amplifier. Axis mechanical binding or collision causing overcurrent.

How do I fix FANUC alarm 427?

1. Check DGN 200 and 204 on the Fanuc diagnosis screen for the specific servo sub-alarm. 2. Check the servo amplifier for fault LEDs and displayed fault codes. 3. Inspect encoder cable and connectors for the affected axis. 4. Manually move the axis with servo off to check for mechanical binding. 5. Power cycle the machine completely to reset the servo system.

axismd.ai

FANUC Controller

Servo/Axis · Intermediate · 30-60 minutes

Alarm 427

Fanuc Alarm 427 - SERVO ALARM: n AXIS EXCESS TORQUE

Fanuc Alarm 427 EXCESS TORQUE occurs when the servo motor's actual torque exceeds the threshold set in parameter 2112 (excessive load detection level). This typically indicates mechanical binding, collision, incorrect load-to-motor matching, or servo tuning issues causing the amplifier to demand excessive current to maintain position.

FANUCServo/AxisIntermediate30-60 minutes

427

Fanuc Alarm 427 - SERVO ALARM: n AXIS EXCESS TORQUE

SERVO ALARM: n AXIS EXCESS TORQUE

Root Cause Summary

Fanuc Alarm 427 EXCESS TORQUE occurs when the servo motor's actual torque exceeds the threshold set in parameter 2112 (excessive load detection level). This typically indicates mechanical binding, collision, incorrect load-to-motor matching, or servo tuning issues causing the amplifier to demand excessive current to maintain position.

Causes and Fixes

1
Navigate to DIAGNOSIS > SERVO > CURRENT (screen varies: 300 series uses DIAGNOSIS #200-207) to observe real-time load meter for affected axis. Check if torque percentage approaches or exceeds parameter 2112 setting (default 300-500%).
2
Put machine in EMERGENCY STOP, manually rotate axis ballscrew or inspect way surfaces for binding, chips, collision damage, or lubricant starvation. Check coupling integrity between motor and ballscrew.
Ensure all power is isolated before manual inspection
3
Inspect axis mechanicals: ballscrew bearing preload, gibs (if box ways), linear guide carriages for damage/contamination. Verify proper lubrication delivery to all sliding surfaces.
4
If collision suspected, review ALARM HISTORY (SYSTEM > ALARM > HISTORY) and check positional error at alarm time in diagnostic #300-302 (position deviation). Large sudden deviation indicates crash.

DIY Feasiblehigh confidence

Call a technician if:

·Motor or amplifier replacement needed
·Ballscrew replacement required
·Encoder failure confirmed
·Multiple axes affected simultaneously

Prevention

Regular lubrication maintenance
Proper cutting parameter selection
Tool condition monitoring
Periodic servo performance verification
Collision detection system calibration

Common Mistakes

Ignoring gradual torque increase trends
Setting torque limits too high for safety
Not checking mechanical condition before parameter changes
Running at 100% feedrate after alarm without investigation
Assuming software issue when mechanical problems exist

Related Alarms

414 415 416 426 428 435

Seeing Multiple Alarms?

Seeing another alarm with this one? Enter the code.

Get machine-aware diagnosis

AxisMD logs alarms against your actual machines, tracks patterns, and gives AI context your manual doesn't have.

Start free

Was this guide helpful?

Always verify with your machine manual or a certified technician before performing service procedures.