Top Mitsubishi CNC Error Codes Explained & How To Fix

Mitsubishi CNC controls such as MELDAS M80/M800, M700/E70, and M60/M70 series use structured alarm codes to report faults across servo, spindle, I/O, communication, memory, and drive systems. Alarms may appear as numeric values or with prefixes like Y, S, or AL. These messages point to concrete electrical, mechanical, or control-state problems rather than abstract software errors.

Alarm Y03 – AXIS NOT CONNECTED

What it means
The control detects that the specified axis is not connected or not responding.

Common causes

• Servo amplifier not powered
• DC link missing on the drive
• Serial communication bus interruption

How to fix

• Confirm servo amplifier power and status LEDs
• Verify DC link voltage on the drive
• Inspect and reseat serial communication cables

Alarm Y06 – PARAMETER ERROR

What it means
An invalid or inconsistent CNC parameter was detected.

Common causes

• Corrupted parameter memory
• Incorrect parameter restore

How to fix

• Restore a known-good parameter backup
• Verify parameters against the machine builder configuration

Servo Alarm S01 – OVERCURRENT / SERVO FAULT

What it means
The servo drive detected excessive current or an internal fault.

Common causes

• Mechanical binding or axis crash
• Encoder feedback problem
• Power supply imbalance
• Internal drive fault

How to fix

• Inspect axis mechanics for binding or damage
• Check encoder cables and connectors
• Verify stable and balanced three-phase power

Servo Alarm S03 – OVERLOAD

What it means
The servo motor was overloaded during motion.

Common causes

• Heavy cutting load
• Mechanical resistance
• Improper servo tuning

How to fix

• Reduce feedrate or cutting depth
• Inspect ballscrews, guides, and lubrication
• Review and adjust servo tuning parameters

Servo Alarm S04 – AD CONVERTER FAULT

What it means
The analog-to-digital converter inside the servo drive is malfunctioning.

Common causes

• Power supply instability
• Failed AD converter circuitry

How to fix

• Check power supply voltages feeding the drive
• Replace the drive if the fault persists

Alarm 0001 – DOG OVERRUN

What it means
The axis passed the reference near-point during homing.

Common causes

• Near-point switch misaligned
• Incorrect reference return parameters

How to fix

• Adjust the near-point switch position
• Correct reference return configuration

Alarm 0002 – INVALID RETURN

What it means
An invalid direction was used during reference return.

Common causes

• Operator error during homing
• Reference configuration mismatch

How to fix

• Perform reference return in the correct direction
• Verify reference settings for the axis

Alarm AL10.1 – UNDERVOLTAGE

What it means
Supply voltage dropped below the allowable threshold.

Common causes

• Power source instability
• Phase loss or weak supply

How to fix

• Measure incoming line voltage
• Correct power supply issues or add stabilization

Alarm AL12 – MEMORY ERROR

What it means
Internal memory corruption detected in the servo drive.

Common causes

• Power interruption during write operation
• Aging or damaged memory components

How to fix

• Restore factory settings on the drive
• Reload parameters and configuration

Alarm AL16 / AL20 – ENCODER FAULT

What it means
Encoder feedback signal error detected by the drive.

Common causes

• Loose or damaged encoder cable
• Encoder hardware failure

How to fix

• Inspect and reseat encoder connectors
• Replace encoder if signal remains unstable

Alarm AL30 – REGENERATIVE BRAKE FAULT

What it means
A fault was detected in the regenerative braking circuit.

Common causes

• Failed braking resistor
• Excessive regenerative current

How to fix

• Inspect braking resistor and wiring
• Replace faulty braking components

Alarm AL37 – SERVO PARAMETER ERROR

What it means
Servo drive parameters are invalid or corrupted.

Common causes

• Incorrect parameter load
• Electrical interference

How to fix

• Reinitialize servo parameters
• Reload correct parameter set

Alarm AL31.1 – MOTOR OVERSPEED

What it means
Motor speed exceeded the configured limit.

Common causes

• Excessive command frequency
• Incorrect acceleration or deceleration settings
• Encoder signal errors

How to fix

• Reduce command frequency
• Adjust acceleration and deceleration parameters
• Inspect encoder integrity

Alarm AL52 – DEVIATION COUNTER EXCEEDED

What it means
Position deviation exceeded the allowable range.

Common causes

• Mechanical shock or looseness
• Encoder malfunction
• Unstable servo tuning

How to fix

• Inspect mechanics for looseness or damage
• Check encoder feedback stability
• Retune servo gains if necessary

Alarm AL.E6 – EMERGENCY STOP

What it means
Emergency stop or safety circuit is active.

Common causes

• Emergency stop button engaged
• Safety circuit wiring open

How to fix

• Release emergency stop devices
• Trace and repair safety circuit wiring

Practical notes for Mitsubishi CNC controls

Mitsubishi CNC alarms almost always indicate a real condition in the machine, drive, or power system. Servo and feedback-related alarms typically point to encoder signal integrity, cabling, or mechanical resistance rather than software faults. Power and undervoltage alarms should be treated as supply quality issues first, especially on older installations. Reference return and homing alarms usually come down to sensor alignment and configuration. Use Mitsubishi diagnostics and drive status information to identify whether the issue is electrical, mechanical, or parameter-related before replacing components.

About MDCplus

Our key features are real-time machine monitoring for swift issue resolution, power consumption tracking to promote sustainability, computerized maintenance management to reduce downtime, and vibration diagnostics for predictive maintenance. MDCplus's solutions are tailored for diverse industries, including aerospace, automotive, precision machining, and heavy industry. By delivering actionable insights and fostering seamless integration, we empower manufacturers to boost Overall Equipment Effectiveness (OEE), reduce operational costs, and achieve sustainable growth along with future planning.