Which of the following statements accurately describes diagnostic latching when a diagnostic fault is detected?

• A. If any diagnostic faults are detected, a fault bit is set, fault data is multicast to all controllers, and the I/O module LED displays a fault.
• B. A fault bit is set and can be examined only on the local module.
• C. If a fault occurs, the system automatically shuts down.
• D. Diagnostics are ignored until a manual reset.

Answer: (A)

Diagnostic latching means the system not only detects a fault but records and communicates it so the fault state is preserved and visible across the network. When a diagnostic fault is detected, a fault bit is set and latched, so the condition remains indicated even if the transient fault clears. That diagnostic information is multicast to all controllers on the network, enabling coordinated awareness and response, not just local visibility. The I/O module LED also signals the fault locally, providing a quick, at-a-glance indication.

Other behaviors don’t fit this pattern: a fault that is only visible on the local module doesn’t leave the network-wide visibility intact; automatic shutdown isn’t implied by diagnostics alone and depends on fault severity and configuration; and ignoring diagnostics until a manual reset isn’t how a latched diagnostic typically operates, since the fault state is retained until it’s acknowledged or cleared.