This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
When Miles O'Brien, Data and Deanna Troi, taken over by Ux-Mal criminals, wanted to make sure that nobody could use the transporter to beam them back to Mab-Bu VI, O'Brien took the entire transporter array off line and placed the transporter in a diagnostic mode which would take hours to complete its cycle. (TNG: "Power Play")
Types of diagnostic modes
Level 1 diagnostic
A level 1 diagnostic was a troubleshooting/test series that required taking the associated system off-line.
One of several peculiarities that allowed William T. Riker to discover that his "future" was actually a fabricated reality was noticing that a level 1 diagnostic Geordi La Forge had apparently been running had lasted for more than thirty hours. This displayed an uncharacteristic level of incompetence, as the same diagnostic would have never taken the real La Forge more than four hours to complete. (TNG: "Future Imperfect")
Level 2 diagnostic
Level 3 diagnostic
Lieutenant Farrell requested permission from Geordi La Forge to run a level 3 diagnostic on the USS Enterprise-D's port plasma relays, as she had noticed one of the generators was fluctuating. (Star Trek Generations)
Level 4 diagnostic
Locking a starship's transporters diagnostic mode, effectively putting it into a diagnostic cycle, would keep any inert matter in the pattern buffer. Ordinarily, inert matter could only remain in the pattern buffer for seven minutes before becoming irretrievably lost, but Montgomery Scott was able to reconfigure a transporter aboard the USS Jenolan, locking the pattern into a level 4 diagnostic cycle to keep his pattern in the pattern buffer for seventy-five years. His pattern was retrieved with minimal degradation. However, another occupant, Ensign Matt Franklin, was not so lucky, his pattern having degraded beyond all hope of retrieval. (TNG: "Relics")
Level 5 diagnostic
Level 10 diagnostic
In 3189, after the USS Discovery computer started behaving strangely, Captain Saru requested the computer run a level ten diagnostic. Upon completion of the diagnostic, the computer responded that it was fully operational. (DIS: "Forget Me Not")
- Security diagnostic (DS9: "Behind the Lines")
- Complete systems diagnostics (VOY: "Parallax")
- Transtator assembly diagnostic (VOY: "Time and Again")
- Diagnostic and Repair Technician, Junior Grade
- Diagnostic array
- Diagnostic subroutine
- Diagnostic team
- Jupiter Station Diagnostic Program Alpha-11
From the entry "diagnostic" in the Star Trek Encyclopedia (4th ed., vol. 1, p. 208), "Engineering analysis programs used aboard Federation starships, intended to permit automated determination of system performance and identification of any malfunctions. Most key systems had a number of such programs available, ranging from level-5 diagnostics (the fastest, most automated) to level-1 diagnostics (the most thorough, but the slowest, requiring the most manual labor)."