Fanuc alarm SP9021: POS SENSOR POLARITY ERROR
spindle alarm (serial spindle, alpha i) · Fanuc 0i-D
What it means
The polarity relationship of the position sensor signals is incorrect, typically because polarity-related bits in parameter No.4000#0 or No.4001#4 do not match the installed sensor and motor rotation direction. The amplifier detects the contradiction during initial rotation checks.
Likely causes
- Sensor polarity parameters changed or never matched after motor/sensor replacement
- Wrong sensor fitted for the motor model
- Feedback cable wired differently than assumed
Need the part urgently?
Send us alarm SP9021 with your machine details — typical RFQ turnaround is 24–48h.