ABB ACS180, Hardware Manual, Page: 157 / 168

Fault tracing
The indications given during the normal operation of the Safe torque off function
are selected by drive control program parameter 31.22.
The diagnostics of the Safe torque off function cross-compare the status of the
two STO channels. In case the channels are not in the same state, a fault reaction
function is performed and the drive trips on an FA81 or FA82 fault. An attempt to
use the STO in a non-redundant manner, for example activating only one channel,
will trigger the same reaction.
See the firmware manual of the drive control program for the indications generated
by the drive, and for details on directing fault and warning indications to an output
on the control unit for external diagnostics.
Any failures of the Safe torque off function must be reported to ABB.
The Safe torque off function 157