Fanuc spindle alarm 06 (AL-06) means the spindle motor's temperature sensor signal is abnormal — the sensor itself is faulty or its cable is broken. Where AL-01 says ‘the motor reads too hot’, AL-06 says ‘the temperature reading itself makes no sense’ — open circuit, out-of-range value, or a sensor type the drive was not told to expect. The motor is almost always physically fine; the measurement chain is broken. Fanuc lists four suspects, and their order is worth respecting because it runs from free to expensive.
Cause 1 — Motor-specific parameters wrong (check first — it's free)
The drive must know which motor — and therefore which temperature sensor characteristic — it is reading. Wrong motor-specific parameters make a healthy sensor read as ‘abnormal’.
- Check the motor-specific parameters against the FANUC AC Spindle Motor αi Parameter Manual (B-65280EN) — in particular the motor model code (parameter 4133) and the sensor-related settings it auto-loads.
- Prime suspects for a parameter cause: the alarm appeared immediately after an amplifier swap, a control-board replacement, or a parameter restore — especially from another machine (see our wrong-data guide). If the machine ran for years and AL-06 appeared out of nowhere, parameters are unlikely — move to the cable.
Cause 2 — The feedback cable (the most common physical cause)
The temperature sensor's conductors travel inside the spindle feedback cable — the same loom as the speed/position sensor signals. A broken conductor, oil-rotted section, or corroded connector pin opens the sensor circuit.
- Power OFF and reseat the feedback connectors at the amplifier (JYA-side) and at the motor; inspect for bent pins, coolant inside the shells, and green corrosion.
- Inspect the run end to end: drag-chain crush points, oil-swollen jacket near the motor, rub-through at cabinet edges. Wiggle-test while watching the display — an alarm that flickers with cable movement is a broken strand.
- Meter the sensor conductors for continuity at both ends (disconnected), flexing at suspect points — broken strands inside intact insulation pass a static test and fail in motion.
- Confirmed or strongly suspected → replace the cable. The same checks (and the same cable) as in our AL-73 guide — the two alarms are neighbours on the same loom, and a cable bad enough for one often produces the other intermittently.
Cause 3 — The amplifier's control PCB
If parameters are right and the cable tests clean, the temperature-sensing input on the spindle amplifier's control board has failed. Fanuc's remedy is ‘replace the control PCB or the amplifier’; the economical path is board-level repair of the sensing input stage — a routine fix on SPM and αi SP units. A quick confirmation when a second machine or spare exists: swap only the amplifier — if AL-06 stays with the machine, it's cable/motor; if it travels with the unit, it's the board.
Cause 4 — The thermo sensor in the motor itself
Last and least common: the embedded sensor has genuinely failed (open). Measure the sensor circuit's resistance at the motor's feedback connector against the motor spec — an open reading with a good cable confirms it. Fanuc's remedy is ‘replace the motor (thermo sensor)’ — in practice the sensor is replaceable during a motor rewind/service without buying a complete motor, which is a fraction of the cost.
Diagnosis checklist (in order)
- Recent amplifier/board/parameter work? → verify motor code 4133 and motor-specific parameters first.
- Reseat and inspect the feedback cable; wiggle-test; meter the sensor conductors.
- Cable clean → amplifier sensing input (swap-test if possible; else bench test).
- Board clean → measure the thermo sensor at the motor connector; open = sensor replacement at rewind service.
- After the repair, verify the motor's temperature reading rises plausibly during a warm-up run — a reading stuck at ambient means the chain still has a break.
Related guides
- Fanuc spindle alarm 01 (motor overheat)
- Fanuc spindle alarm 73 (motor sensor disconnected)
- Fanuc “wrong data is used” error guide
- Fanuc αi drive alarms — PSM, SVM & SPM codes explained