Alarm guide · Fanuc · Updated October 2026
Fanuc SV0438 alarm: inverter abnormal current
Fanuc SV0438 means abnormal current in the servo amplifier (inverter). A short or insulation fault in the motor or power cable is a common cause.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The amplifier saw current outside the normal range in its power stage. Alarm numbers and wording can differ between series, so confirm with the manual for your unit.
Common causes
- Motor winding short or insulation breakdown
- Motor power cable fault
- Amplifier power module fault
- Wrong parameter
- Moisture or coolant inside the motor
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
Test the motor insulation and winding. Disconnect the power cable first and check it separately.
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 Fanuc servo motor repair, Fanuc encoder repair and Fanuc servo drive repair.
Questions
How do I know if it is the motor?
An insulation and winding test on the motor and cable separates the motor from the amplifier.
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: SV0414 · SV0364 · SV0368 and SV0366
Brand names identify the units we repair. Star Automations is an independent multi-brand repair company and is not an OEM service centre.