Code SP0021: Position sensor polarity setting incorrect
Issue Description & Safety Warning
The Fanuc Alpha-i Servo Spindle Amplifier has triggered a critical Position sensor polarity setting incorrect alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Amplifier LED display: 21 Also shown as: SP0021 (15i), SP9021 (30i/31i/32i), SP9021 (0i-D) Cause: The specified polarity of the position sensor is incorrect. Troubleshooting when this alarm is issued (a) Check the position sensor polarity parameter (bit 4 of parameter No. 4001). (b) Check the feedback cable of the position sensor.
Source: Fanuc αi Servo/Spindle Amplifier Maintenance Manual (B-65285EN/04) — Part II Troubleshooting
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Fanuc Alpha-i Servo Spindle Amplifier Alarms
Fanuc controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code SP0021 on the Alpha-i Servo Spindle Amplifier identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Fanuc's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 135 Fanuc Alpha-i Servo Spindle Amplifier codes.
Have a better solution?
Help the industrial community by sharing your repair experience for code SP0021.
Need a searchable reference for more Fanuc Alpha-i Servo Spindle Amplifier manuals?
We structure equipment manuals into searchable code, title, cause, solution, safety note, and source-reference data. Send a PDF and example searched codes when you need public pages, private search, or structured exports.
Space reserved for Google AdSense / Industrial Affiliate Links
Monetization target for 2026