Fanuc spindle alarm d4 means a change in position data from the serial sensor exceeded the expected range — the reported position jumped further between samples than physics allows. The sensor is effectively claiming the spindle teleported. Fanuc's triage: at start-up, both (a) and (b) apply; on a machine that has been operating normally, the cause is (b).
The two causes
- (a) Parameter setting error (first start only): wrong sensor-setting parameters make the amplifier misinterpret the data stream — legitimate readings decode as jumps. Check per the ‘Parameters Related to Start-up’ section of B-65280EN. The usual arrival route: restores and amplifier swaps.
- (b) Cable shielding — the running-machine cause: noise corrupting the serial stream produces impossible position steps — the same physics as d3, caught by a different check. Verify shield continuity, correct termination, and routing away from power leads per the ‘Detectors’ section of B-65282EN.
Tip: d3 and d4 are two symptoms of one disease on a running machine — noise on the serial sensor link. Fix the shielding once, properly (continuity, clamp termination, separation), and both disappear. If they persist after genuinely clean cabling, the sensor's own electronics are the next suspect — see d9 territory — then the amplifier's receiver.
Related guides
- Fanuc spindle alarm d3 (data destroyed by noise)
- Fanuc spindle alarm d9 (sensor inner circuit)
- Fanuc spindle alarm d2 (serial sensor disconnected)
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