J

Over-heat of Resistor Module (ECM)

Fanuc · Alpha i Series AC Servo Motor and Spindle

What does J mean?

The Resistor Module has detected an abnormal temperature, indicating overheating. This is typically detected by a built-in thermostat.

Common Causes

  • The temperature of the braking resistor module has exceeded its safe operating limit.
  • Braking resistor is continuously subjected to high power dissipation.
  • Inadequate cooling or ventilation of the braking resistor assembly.
  • Faulty temperature sensor within the braking resistor module.
  • Overload condition causing excessive regenerative energy.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check for blockages to airflow around the Resistor Module.

  2. 2

    Verify the operation of any cooling fans associated with the Resistor Module.

  3. 3

    Ensure the discharge duty cycle is within specifications; excessive regeneration can cause overheating.

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Verified technical data. Last updated: March 2026

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Source: Fanuc Alpha i Series AC Servo Motor and Spindle