In SRP/CS safety functions, which statement correctly contrasts diagnostic coverage with the proof test interval?

• A. Diagnostic coverage describes testing frequency.
• B. Diagnostic coverage is fault detection capability; proof test interval is how often testing occurs.
• C. Diagnostic coverage is how fast faults are repaired; proof test interval is how long the system has existed.
• D. Diagnostic coverage is related to hardware redundancy; proof test interval is unrelated to safety.

Answer: (B)

Diagnostic coverage describes the fault detection capability of the safety function’s diagnostics during operation—how reliably faults are actually caught by the onboard diagnostics. The proof test interval is the time between independent re-tests of the safety function to verify its correct operation, including revealing latent faults that the diagnostics might miss. These two aspects address different parts of safety assurance: diagnostics detect faults as the system runs, while proof tests periodically validate the overall safety behavior.

So the statement that diagnostic coverage is fault detection capability and the proof test interval is how often testing occurs captures this distinction accurately. Describing diagnostic coverage as testing frequency would miss that it’s about how effectively faults are detected, not just how often tests happen. The other options mix in concepts like repair speed, system age, or hardware redundancy, which are not what diagnostic coverage or proof test interval define.