Alarm guide · Mitsubishi · Updated October 2026
Mitsubishi AL.46 alarm: servo motor overheat
Mitsubishi AL.46 means the motor thermal protector tripped: the servo motor overheated. Look at the load, ambient temperature and the motor condition.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The motor temperature sensor reported a temperature above its limit. Alarm numbers and wording can differ between series, so confirm with the manual for your unit.
Common causes
- Load or duty above the motor rating
- High ambient temperature or poor airflow
- Dirt or oil on the motor body
- Bearing friction or a winding fault
- Thermal sensor wiring fault
Safe first checks
General guidance only. Follow the drive manual and your site's electrical safety rules. Power off, and let the DC bus discharge, before touching connectors.
- Note the exact alarm code and when it appears: at power-up, at start, or under load.
- Power off and turn the shaft by hand if safe: it should turn smoothly.
- Check the motor cable, encoder cable and connectors for damage and loose contacts.
- Check what changed recently: load, speed, settings, cables or a replaced part.
When to send it for repair
A motor that overheats on a free mechanism needs inspection: bearings, winding and the thermal sensor.
We test every motor on our Universal Servo Motor Repair Equipment, which reads and aligns the feedback and runs the motor under load without the original drive.
See Mitsubishi servo motor repair, Mitsubishi encoder repair and Mitsubishi servo drive repair.
Questions
Will it cool and work again?
It may, but the cause remains. Repeated overheating shortens winding and bearing life.
How long does repair take?
Emergency repair is done the same day where the fault and parts allow, urgent in 3 working days and standard in 7 working days, counted from when the unit reaches our bench and the quote is approved. Every unit returns with a printed test report.
Can I get an exchange unit?
If we hold a matching unit, Servo Swap ships a tested exchange unit while yours is repaired. Mark "line down" on the request form and add the part number.
Related: AL.25 · AL.50 · AL.16 and AL.20
Brand names identify the units we repair. Star Automations is an independent multi-brand repair company and is not an OEM service centre.