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Check coolant flow rate at the spindle motor inlet and outlet connections. Verify flow meets manufacturer specifications (typically 15-25 liters/minute for most spindles).

Inspect heat exchanger operation. Check coolant inlet temperature (should be 15-20°C), verify chiller compressor is running, and check for clogged heat exchanger fins or internal passages.

Examine coolant filter and clean or replace if clogged. Check all coolant lines for kinks, blockages, or debris restricting flow.

Ensure machine power is off before disconnecting coolant lines to prevent spills.

Verify coolant pump is operating at correct pressure (typically 2-4 bar). Listen for abnormal pump noise indicating cavitation or bearing failure.

Access spindle drive diagnostics screen and check actual coolant temperature reading. Compare to physical temperature measured at spindle housing with infrared thermometer.

Disconnect temperature sensor connector at spindle motor. Measure resistance across sensor terminals (PT100 should read approximately 100-120 ohms at room temperature; thermistor typically 2-10k ohms depending on type).

Tag and photograph connector orientation before disconnecting to ensure correct reconnection.

Check continuity and insulation resistance of wiring from spindle motor temperature sensor to spindle drive module. Look for damaged cable in cable track or at connectors.

If sensor tests faulty, replace with exact OEM replacement. After replacement, verify correct parameter settings for sensor type (parameter 4025 for sensor type selection).

Using incorrect sensor type or parameters will cause immediate alarm recurrence.

Review alarm history and check if alarm occurs during specific operations or after extended run time. Monitor spindle load percentage during operation (should not exceed 80% continuously).

Check ambient temperature in electrical cabinet and around spindle motor. Ensure cabinet cooling fans are operational and air filters are clean. Verify ambient temperature is within specification (typically below 40°C).

Verify coolant temperature alarm threshold parameter (typically parameter 4023 or 4033, set around 45-55°C). Confirm setting matches spindle motor specifications and has not been incorrectly modified.

Do not simply increase the alarm threshold without addressing root cause, as this risks spindle motor damage.

If alarm persists under normal load conditions, examine spindle motor bearings for wear. Excessive bearing friction generates heat. Check for abnormal noise, vibration, or play in spindle shaft.

Worn spindle bearings require immediate attention to prevent catastrophic failure.