Code STo: Motor Pull Out or Step Out Detection
Issue Description & Safety Warning
The Yaskawa A1000 AC Drive has triggered a critical Motor Pull Out or Step Out Detection 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
Code type: Fault Manual section: Yaskawa A1000 Troubleshooting The wrong motor code is set (Yaskawa motors only). - Enter the correct motor code for the PM being used into E5-01. - For special-purpose motors, enter the correct data to all E5 parameters according to the test report provided for the motor. Load is too heavy. - Increase the load inertia for PM motor (n8-55). - Increase the pull-in current during accel/decel (n8-51). - Reduce the load. - Increase the motor or drive capacity. Load inertia is too heavy. Increase the load inertia for PM motor (n8-55). Acceleration and deceleration times are too short. - Increase the acceleration and deceleration times (C1-01 through C1-08). - Increase the S-curve acceleration and deceleration times (C2-01). Speed response is too slow. Increase the load inertia for PM motor (n8-55).
Source: Yaskawa AC Drive A1000 High Performance Vector Control Drive Technical Manual (SIEP C710616 21H)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Yaskawa A1000 AC Drive Alarms
Yaskawa controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code STo on the A1000 AC Drive identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Yaskawa's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 280 Yaskawa A1000 AC Drive codes.
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