Stuck-at-fault by STC

Hi,

In page 346 (8.4.10) of TRM (spnu499), "Insert stuck-at-fault inside CPU so that STC signature compare will fail" is described.
I want to know what the fault is inserted, how the fault is inserted, where the fault is inserted and what happened by insertion of the fault, I must discuss it whether it is safety or not with my customers.
Could you explain the flow from the insertion of the fault to the detection of it?

Thanks

Nomoto