Cause : STO Loss 3 comes when STO1 and SCM1, or STO2 and SCM2 short circuit lines are not connected or the IO card does not match the version of the control board.

The STL2 fault in Delta drive indicates a Safe Torque Off (STO) Loss on channel 3 error. This STO function is a critical safety mechanism designed to prevent unexpected motor rotation and potential hazards.