Guide · Mitsubishi · MELSERVO-J4 · Updated November 2026
Mitsubishi servo drive alarm list (MR-J4): alarm and warning codes
A Mitsubishi MELSERVO-J4 amplifier shows an alarm or warning number on its display when it detects a fault. This page lists the numbers with the names given in Mitsubishi Electric's troubleshooting manual, and links to our detailed guide for the common ones. Alarm numbers differ between amplifier series, so confirm against the manual for your exact amplifier. Star Automations repairs Mitsubishi servo amplifiers and is an independent repairer, not a Mitsubishi Electric authorised service provider.
First checks when the amplifier shows an alarm
- Note the alarm number, including any detail number after the dot, and photograph the display.
- Check the amplifier model and the servo motor model from the nameplates.
- Check the incoming supply, the regeneration resistor and the cooling fan.
- Check the encoder cable and connectors for damage or loose pins.
- Isolate the power and wait until the charge lamp is off before opening the amplifier.
- After alarms 30, 45, 46, 50 and 51, remove the cause and allow about 30 minutes for cooling before restarting. Do not cycle the power repeatedly.
Mitsubishi MR-J4 alarm numbers
| No. | Alarm name | Our guide |
|---|---|---|
| 10 | Undervoltage | Guide |
| 11 | Switch setting error | |
| 12 | Memory error 1 (RAM) | |
| 13 | Clock error | |
| 14 | Control process error | |
| 15 | Memory error 2 (EEP-ROM) | |
| 16 | Encoder initial communication error 1 | Guide |
| 17 | Board error | |
| 19 | Memory error 3 (Flash-ROM) | |
| 1A | Servo motor combination error | |
| 1B | Converter error | |
| 1E | Encoder initial communication error 2 | |
| 1F | Encoder initial communication error 3 | |
| 20 | Encoder normal communication error 1 | Guide |
| 21 | Encoder normal communication error 2 | |
| 24 | Main circuit error | |
| 25 | Absolute position erased | Guide |
| 27 | Initial magnetic pole detection error | |
| 28 | Linear encoder error 2 | |
| 2A | Linear encoder error 1 | |
| 2B | Encoder counter error | |
| 30 | Regenerative error | Guide |
| 31 | Overspeed | Guide |
| 32 | Overcurrent | Guide |
| 33 | Overvoltage | Guide |
| 34 | SSCNET receive error 1 | |
| 35 | Command frequency error | |
| 36 | SSCNET receive error 2 | |
| 37 | Parameter error | |
| 39 | Program error | |
| 3A | Inrush current suppression circuit error | |
| 3D | Parameter setting error for driver communication | |
| 3E | Operation mode error | |
| 42 | Servo control error (linear servo motor and direct drive motor) / Fully closed loop control error | |
| 45 | Main circuit device overheat | Guide |
| 46 | Servo motor overheat | Guide |
| 47 | Cooling fan error | |
| 50 | Overload 1 | Guide |
| 51 | Overload 2 | Guide |
| 52 | Error excessive | Guide |
| 54 | Oscillation detection | |
| 56 | Forced stop error | |
| 61 | Operation error | |
| 63 | STO timing error | |
| 64 | Functional safety unit setting error | |
| 65 | Functional safety unit connection error | |
| 66 | Encoder initial communication error (safety observation function) | |
| 67 | Encoder normal communication error 1 (safety observation function) | |
| 68 | STO diagnosis error | |
| 69 | Command error | |
| 70 | Load-side encoder initial communication error 1 | |
| 71 | Load-side encoder normal communication error 1 | |
| 72 | Load-side encoder normal communication error 2 | |
| 74 | Option card error 1 | |
| 75 | Option card error 2 | |
| 79 | Functional safety unit diagnosis error | |
| 7A | Parameter setting error (safety observation function) | |
| 7B | Encoder diagnosis error (safety observation function) | |
| 7C | Functional safety unit communication diagnosis error (safety observation function) | |
| 7D | Safety observation error | |
| 82 | Master-slave operation error 1 | |
| 84 | Network module initialization error | |
| 85 | Network module error | |
| 86 | Network communication error | |
| 8A | USB / serial / Modbus RTU communication time-out error | |
| 8D | CC-Link IE communication error | |
| 8E | USB / serial / Modbus RTU communication error | |
| 888 | Watchdog |
Names follow the MELSERVO-J4 Servo Amplifier Instruction Manual (Troubleshooting) published by Mitsubishi Electric; a few long combined names are shortened. Detail numbers, causes and actions for each alarm are in that manual: open the manual (PDF).
Mitsubishi MR-J4 warning numbers
| No. | Name in the manual |
|---|---|
| 90 | Home position return incomplete warning |
| 91 | Servo amplifier overheat warning |
| 92 | Battery cable disconnection warning |
| 93 | ABS data transfer warning |
| 95 | STO warning |
| 96 | Home position setting warning |
| 97 | Positioning specification warning |
| 98 | Software limit warning |
| 99 | Stroke limit warning |
| 9A | Optional unit input data error warning |
| 9B | Error excessive warning |
| 9C | Converter error |
| 9D | CC-Link IE warning 1 |
| 9E | CC-Link IE warning 2 |
| 9F | Battery warning |
| E0 | Excessive regeneration warning |
| E1 | Overload warning 1 |
| E2 | Servo motor overheat warning |
| E3 | Absolute position counter warning |
| E4 | Parameter warning |
| E5 | ABS time-out warning |
| E6 | Servo forced stop warning |
| E7 | Controller forced stop warning |
| E8 | Cooling fan speed reduction warning |
| E9 | Main circuit off warning |
| EA | ABS servo-on warning |
| EB | The other axis error warning |
| EC | Overload warning 2 |
| ED | Output watt excess warning |
| F0 | Tough drive warning |
| F2 | Drive recorder - Miswriting warning |
| F3 | Oscillation detection warning |
| F4 | Positioning warning |
| F5 | Simple cam function - Cam data miswriting warning |
| F6 | Simple cam function - Cam control warning |
| F7 | Machine diagnosis warning |
Names are taken from the same Mitsubishi Electric troubleshooting manual. Your amplifier type and software version may show a different set.
Amplifier, motor or cable?
Encoder alarms (16, 20, 21, 25)
Check the encoder cable and connector first, then the absolute position backup battery where it applies, then the encoder. See AL.16 and AL.20 and AL.25.
Overcurrent (32)
Can be the amplifier power stage, the motor or the cable. Disconnect the motor and see whether the alarm stays. See AL.32.
If the alarm stays after these checks, see Mitsubishi servo drive repair, Mitsubishi servo motor repair and Mitsubishi encoder repair.
Mitsubishi servo alarm questions
What does an alarm number on a Mitsubishi MR-J4 amplifier mean?
The number on the amplifier display identifies the fault the amplifier detected, such as undervoltage (10), an encoder communication error (16, 20), overcurrent (32) or overload (50, 51). Some numbers also carry a detail number after the dot. Mitsubishi Electric lists them in the MELSERVO-J4 Servo Amplifier Instruction Manual (Troubleshooting).
Do these numbers apply to MR-J2S, MR-J3 and MR-JE amplifiers?
Alarm numbers and detail codes can differ between series. This list follows the MELSERVO-J4 troubleshooting manual. For another series, use the manual for your exact amplifier.
Does AL.16 or AL.20 mean the servo motor is faulty?
Not necessarily. The manual lists causes such as a faulty encoder cable, an amplifier or encoder fault, and noise. Check the cable and connector first, then test the encoder.
Can I reset the alarm and restart straight away?
Not while the cause is still present. The manual says not to cycle the power repeatedly to restart after alarms 30, 45, 46, 50 or 51; remove the cause and allow about 30 minutes for cooling first.
What is the difference between an alarm and a warning?
Mitsubishi lists alarms (for example 10, 16, 32) and warnings (for example 91, E1, E6) in separate tables. Check the manual table for what your amplifier does for each number.
Do you repair Mitsubishi servo amplifiers and servo motors?
Yes. Star Automations repairs Mitsubishi MELSERVO amplifiers, servo motors and encoders. Send the amplifier label and the alarm number on WhatsApp or by email. Star Automations is an independent repairer and is not a Mitsubishi Electric authorised service provider.
Send the alarm number and amplifier model.
WhatsApp a photo of the amplifier label and the display to +91 97866 22233, or email info@starautomations.com.