Code SP0042: Position coder one-rotation signal not detected
Issue Description & Safety Warning
The Fanuc Alpha-i Servo Spindle Amplifier has triggered a critical Position coder one-rotation signal not detected 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: 42 Also shown as: SP0042 (15i), SP9042 (30i/31i/32i), SP9042 (0i-D) Cause: The one-rotation signal of the αi position coder is not generated. Troubleshooting when this alarm is issued (a) The setting of a parameter is incorrect. Referring to "FANUC AC SPINDLE MOTOR αi series Parameter Manual (B-65280EN)," check the parameter for sensor setting. (b) The αi position coder is faulty. Check the check pin PSD on the spindle check board. If the signal is not generated per rotation, replace the connection cable and position coder. (c) The Spindle Amplifier is faulty. Replace the Spindle Amplifier or Spindle Amplifier control printed circuit board.
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 SP0042 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.
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