LS L7NH Fault Codes List

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Troubleshoot your LS Electric L7NH EtherCAT servo drive with our updated guide. Learn to interpret AL-xx alarm codes, use DriveView 9 for diagnostics, and resolve EtherCAT synchronization errors.

L7NH Fault Codes Reference Table

Below is the complete list of alarms and warnings for the L7NH series. Please refer to this table to match the code on your drive’s display with the specific hardware, communication, or tuning diagnostic.

LS L7NH Fault Codes List

LS L7NH Fault Codes List

Fault Code and Meaning Cause and Remedy
AL-10
IPM fault (Over current H/W)		 Cause:
  • Motor or Encoder cable wiring is incorrect or shorted.
  • Parameter setting error (Motor ID, Encoder type/form).
  • Machine part has a problem (conflict or binding).
  • Drive error or Noise interference.

Remedy:
  • Replace motor or encoder cable.
  • Modify the parameter to match motor label information.
  • Check if the machine part has a problem.
  • If alarm continues, replace drive.
  • Check wiring condition for FG (Frame Ground) and match wire size.
AL-11
IPM temperature (Overheating)		 Cause:
  • Ambient temperature is over 50 [°C].
  • Continuous Overload (accumulated load > 100%).
  • High-frequency operation of regenerative drive.
  • Drive setting direction error.

Remedy:
  • Lower surrounding temperature.
  • Change drive and motor capacity or tune gain.
  • Adjust regeneration resistor setting [0x2009] or use external resistor.
  • Refer to wiring and connection manual.
  • If alarm continues, replace drive.
AL-14
Over current (S/W)		 Cause:
Check motor phase resistor (U-V, V-W, W-U).

Remedy:
  • Replace motor.
AL-15
Current offset		 Cause:
Motor U/V/W phase current offset oversetting (are 5% of rated current or higher).

Remedy:
  • Rerun adjusting phase current offset.
  • If alarm occurs continually after adjusting, replace the drive.
AL-16
Current limit exceeded		 Cause:
Drive error or Error by noise.

Remedy:
  • If alarm continues after servo on again, replace drive.
  • Check method to improve noise of wiring/installation.
AL-21
Continuous overload		 Cause:
  • Load exceeds rated load during operation.
  • Motor brake is not holding.
  • Parameter setting error (Motor ID, Encoder type).
  • Machine part has binding/conflict.
  • Motor or Encoder cable wiring incorrect/short.

Remedy:
  • Change drive and motor capacity; please tune gain.
  • Provide supply power to motor brake.
  • Modify parameter to match motor label; set proper overload detecting values.
  • Check machine part for problems.
  • Replace motor or encoder cable.
AL-22
Drive temperature 1		 Cause:
  • Ambient temperature is over 50 [°C].
  • Drive error (Internal temp sensor deviation).

Remedy:
  • Lower the surrounding temperature of drive.
  • Replace the drive.
AL-23
Regeneration overload		 Cause:
  • Capacity excess by high frequency/continuous regenerative operation.
  • Parameter setting error (Regen resistance value).
  • Main power input voltage over 544 [Vac].

Remedy:
  • Adjust value on 0x2009. Use braking resistor.
  • Set parameters [0x2009] ~ [0x200E] to proper values.
  • Recheck the power supply.
  • If regenerative resistance temperature is high in Servo-off, replace drive.
AL-24
Motor cable open		 Cause:
  • Parameter setting error (Phase current offset).
  • Motor cable disconnected.
  • Short circuit of U,V,W in Motor.

Remedy:
  • Process the Phase current offset control procedure command.
  • Replace motor cable.
  • Replace the motor.
AL-25
Drive temperature 2		 Cause:
Ambient temperature over 50 [°C] or Drive error.

Remedy:
  • Lower the surrounding temperature.
  • Replace the drive.
AL-30
Encoder communication		 Cause:
  • Encoder cable wiring incorrect or shorted.
  • Parameter setting error (Motor ID/Type).

Remedy:
  • Replace encoder cable.
  • Modify parameter to match motor label information.
  • If modified value is not applied, change servo motor.
AL-31
Encoder cable open		 Cause:
Encoder error.

Remedy:
  • If alarm continues after servo on again, replace drive.
AL-32
Encoder data		 Cause:
Drive error.

Remedy:
  • If alarm continues after servo on again, replace drive.
AL-33
Motor setting (ID Error)		 Cause:
Setting Motor ID value [0x2000] is same with application motor label.

Remedy:
  • Revise it with motor label information equally.
  • Alarm may release after power off/on following parameter adjustment.
  • If alarm continues, replace drive.
AL-34
Z Phase open		 Cause:
  • Parameter setting error (Warning mask).
  • Encoder cable wiring incorrect or short.
  • Encoder or Drive error.

Remedy:
  • For motors without Z phase (e.g., step motors), mask AL-34 in [0x2014].
  • Replace encoder cable.
  • If alarm continues, replace drive.
AL-35
Low battery		 Cause:
  • Parameter setting error (Absolute encoder value).
  • Poor battery contact or not connected.
  • Battery voltage is low (under 3.3V).

Remedy:
  • If using absolute encoder as incremental, set [0x2005] to 1.
  • Connect battery tightly.
  • Replace battery.
AL-36
Sinusoidal ENC amplitude		 Cause:
  • Encoder cable wiring incorrect/short/shield disconnect.
  • Parameter setting error (Encoder type).
  • Drive error.

Remedy:
  • Replace encoder cable.
  • Check setting encoder type. Check speed command (Max 250kHz).
  • If alarm continues, replace drive.
AL-37
Sinusoidal ENC frequency		 Cause:
Converter error or Encoder error.

Remedy:
  • If alarm continues after servo on again, replace drive.
AL-38
Encoder setting error		 Cause:
  • Drive / Motor combination error (Brand label mismatch).
  • Encoder cable wiring incorrect/short.
  • Encoder or Drive error.

Remedy:
  • Use motor and drive of same brand label.
  • Replace encoder cable.
  • If alarm continues, replace drive.
AL-39
Preset Error		 Cause:
  • Parameter setting Error (Absolute encoder value).
  • Poor battery contact.
  • Initial encoder power supply timing.

Remedy:
  • If using absolute encoder as incremental, set [0x2005] to 1.
  • Connect battery correctly, reset alarm, reapply power. Check mechanical home.
  • Reapply power after alarm reset.
AL-40
Under voltage		 Cause:
  • Main power input voltage error (Over 134 Vac).
  • DC Link voltage error (Value over 190 Vdc).
  • Running when power voltage is low.
  • Main power input below 286 Vac.

Remedy:
  • Recheck the power supply.
  • Replace the drive.
  • Use 3 phase as supply voltage.
AL-41
Over voltage		 Cause:
  • DC link voltage error (Below 405 Vdc).
  • When braking resistor is high.
  • Setting value of acceleration/deceleration is too short.

Remedy:
  • Replace the drive.
  • Review the regenerative resistance considering operating condition/load.
  • Set longer acceleration / deceleration time.
AL-42
Main power fail		 Cause:
  • Main power input voltage error (Phase L1, L2, L3).
  • Parameter setting error (Input mode [0x2006]).
  • Momentary power failure.

Remedy:
  • Recheck the power supply.
  • Wire or set parameter as input power on (possible 3 phase).
  • Check main power source or reduce value of [0x2007].
  • If alarm continues, replace drive.
AL-43
Control power fail		 Cause:
Voltage between phase of C1, C2 is not within 200-230[Vac].

Remedy:
  • Recheck power supply of drive.
  • If alarm continues, replace drive.
AL-50
Over speed limit		 Cause:
  • Motor/Encoder cable wiring incorrect or short.
  • Parameter setting Error (Motor ID/Electronic gear ratio).
  • Encoder or Drive error.

Remedy:
  • Replace motor/encoder cable.
  • Set Electronic gear ratio low.
  • Readjust gain according to operating condition.
  • If alarm continues, replace drive.
AL-51
POS following		 Cause:
  • Parameter setting Error (Gear ratio/Pos error range).
  • Machine part has problem (forced by drive part).

Remedy:
  • Set Electronic gear ratio low.
  • Set up correct parameter according to operating method.
  • Check machine part has problem.
  • If alarm continues, replace drive.
AL-53
Cable Error		 Cause:
  • Motor cable disconnected/wiring incorrect/short.
  • Encoder cable disconnected/wiring incorrect/short.

Remedy:
  • Replace motor cable.
  • Replace encoder cable.
Excessive SPD deviation Cause:
  • Parameter setting Error (Motor ID).
  • Machine part has problem (forced by drive part).
  • Encoder/Drive error.

Remedy:
  • Modify parameter as same as motor label information.
  • Set Electronic gear ratio low.
  • Check machine part has problem.
  • If alarm continues, replace drive.
AL-63
Parameter checksum		 Cause:
When O/S is changed (Parameter setting value set as max value of variable form).

Remedy:
  • Restore initial parameter (0x1011).
  • Set up parameter before operating.
  • If alarm continues, replace drive.
AL-71
Factory setting		 Cause:
Parameter setting error.

Remedy:
  • Contact service center. Check [0x1008] Device Name.
  • Please download OS or set capacity of drive again.
  • If alarm continues, replace drive.
W01 (PWR_FAIL)
Main power input Voltage error		 Cause:
  • Voltage between phase 200-230[Vac] error.
  • Parameter setting error [0x2006].
  • Momentary power failure.

Remedy:
  • Recheck the power supply.
  • Wire or set parameter as input power on.
  • Check actual main power or increase checking time of loss.
  • If alarm continues, replace drive.
W02 (LOW_BATT)
Low voltage of encoder battery		 Cause:
  • Parameter setting error [0x2005].
  • Bad connection of battery.
  • Battery voltage is low (over 3.3V check).

Remedy:
  • Alarm disappears if set to "1" (Incremental mode).
  • Connect battery rightly.
  • Replace battery.
W04 (SW_POS_LMT)
Software Position Limit		 Cause:
Parameter setting error (Software restriction on location [0x2400]).

Remedy:
  • Change value of software position limit function [0x2400].
  • Change limit value of max/min position [0x607D].
W10 (OV_LOAD)
Operation overload		 Cause:
  • Sequent operating exceeding rated load.
  • Motor brake error (not holding).
  • Parameter setting error (Motor ID).
  • Machine part has problem.
  • Cable errors.

Remedy:
  • Change drive and motor capacity, please tune gain.
  • Adjust setting value overload warning level [0x2010].
  • Provide supply power to motor brake.
  • Modify parameter to match motor label.
  • Check machine part.
  • Replace cables.
W20 (SETUP)
Abnormal combination / IO setting		 Cause:
  • Drive / Motor Combination error (Capacity mismatch).
  • IO setting error (Signal assignment duplicate).

Remedy:
  • Reduce value of torque limit or use motor with lower capacity than drive.
  • Set up correct parameter according to operating method.
W40 (UD_VTG)
Low Voltage		 Cause:
  • Main power input voltage error (> 134 Vac).
  • DC link voltage error (190~405 Vdc).
  • Running when power voltage is low.

Remedy:
  • Recheck the power supply.
  • Replace the drive (if DC link error persists).
  • Use 3 phase as supply voltage.
W80 (EMG)
Emergency signal input		 Cause:
EMG contact error / Drive error.

Remedy:
  • Set up correct parameter according to operating method.
  • If alarm continues after servo on again, replace drive.
 

How to Read L7NH Faults via DriveView 9 & EtherCAT Master

Because the L7NH is a networked drive, diagnostics in 2026 often involve looking at both the drive hardware and the EtherCAT master (PLC/Controller) using DriveView 9 software.

  • Alarm History: The L7NH stores a detailed log of the last 16 alarms. DriveView 9 allows you to view these with the precise power-on time, making it easier to identify if AL-5x (Communication) errors are linked to network startups.
  • Object Dictionary (CoE): You can browse the CANopen over EtherCAT objects (e.g., Index 0x603F) to see the exact error code being reported to the PLC. This is critical for remote diagnostics.
  • High-Speed Trace: Capture waveforms of Motor Torque, Velocity, and EtherCAT Sync pulses. This helps identify if an AL-40 (Overload) is caused by mechanical binding or a loss of synchronization with the master controller.

General Troubleshooting Steps for L7NH Servos

Before performing a reset, verify these three critical areas of the EtherCAT servo system:

  1. EtherCAT Network Integrity: For communication alarms (AL-5x or AL-8x), check the IN/OUT RJ45 cables. In 2026, ensure you are using Category 5e or higher shielded cables, as high-frequency noise can cause intermittent sync losses.
  2. Absolute Encoder Battery (AL-24): If you are using an absolute encoder, AL-24 indicates the position data was lost because the backup battery died. You must replace the battery and perform the Absolute Encoder Reset to re-home the axis.
  3. STO (Safe Torque Off): If the drive shows “St” or “Safe”, the STO circuit is open. This is a safety state, not a drive fault. Verify the wiring on the CN1/CN6 safety connector and ensure your safety relay is energized.

Frequently Asked Questions (FAQ)

Q: What is the difference between an Alarm and a Warning on the L7NH?

A: An Alarm (e.g., AL-10) is a major trip that immediately disables the motor (Servo-OFF). A Warning (indicated by a specific code or flashing LED) notifies you that a limit—such as regeneration duty or temperature—is being reached, but the motor continues to run.

Q: How do I reset a fault on the LS L7NH?

A: Once the cause is removed, you can reset the drive by:

  • Pressing the [SET/RESET] key on the front panel.
  • Sending a Fault Reset command (Bit 7 of the Controlword) via EtherCAT.
  • Cycling the control power (L1C, L2C). Note: Hardware faults like AL-10 (Overcurrent) usually require a full power cycle.

Q: Why does my drive show “bb” or “Gr” on the display?

A: bb (Base Block) means the drive is healthy but in standby (Servo-OFF). Gr (Run) means the drive is active and currently controlling the motor. These are status indicators, not faults.

Q: What does “AL-21” (Encoder Communication Error) mean?

A: This indicates a failure to communicate with the motor’s encoder. Check for broken wires in the feedback cable, especially if the axis is part of a moving cable track (flex-cable fatigue). Ensure the encoder connector is fully seated and locked.

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