Diagnostic mode
A computer system's diagnostic mode or diagnostic cycle was used to ascertain whether or not there were problems or inconsistencies in a starship's main systems, including the transporters. A diagnostic engineer specializes in diagnostics.

In 2151,  ran diagnostics in engineering and found a power surge in the transceiver array. ()

In 2153, Tucker ordered Haynem to perform a diagnostic of Shuttlepod 2, as the impulse assembly had taken some damage. ()

In 2368, 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. ()

In 2369, Bajoran engineer Neela ran a diagnostic of modifications she had made before. ()

Types of diagnostic modes

Level 1 diagnostic 
A level 1 diagnostic was a troubleshooting/test series that required taking the associated system off-line.

In 2366 after a control malfunction, Captain Jean-Luc Picard told Geordi La Forge to run a level 1 diagnostic after the computer log showed nothing unusual about that time period. ()

In 2369, Chief Miles O'Brien ran a level 1 diagnostic of the runabout ' systems, including the central power linkages. ()

The same year, he told Julian Bashir that he was thinking of running a level 1 diagnostic of the phase coil generators when he was back aboard space station Deep Space 9. ()

Later, O'Brien ordered Neela to run a level 1 diagnostic of the runabout's computer interface, after they discovered that Ensign Aquino had been murdered there. ()

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. ()

Level 2 diagnostic

Level 3 diagnostic 

On the , level 3 diagnostics of the spore drive were run every ten hours. ()

Lieutenant Farrell requested permission from Geordi La Forge to run a level 3 diagnostic on the 's port plasma relays, as she had noticed one of the generators was fluctuating. ()

In 2369, Commander Benjamin Sisko ordered a quick level 3 diagnostic of the graviton generator because of residual charge readings. ()

The same year, Chief Miles O'Brien ran a level 3 sensor sweep through the promenade to detect anomalous readings after he found the program ANA. ()

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 , 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; due to a phase inducer faliure, his pattern has degraded beyond all hope of retrieval. ()

Level 5 diagnostic 

In 2259, Commander Hemmer was convinced to run a level 5 diagnostic of the 's transporter's pattern buffer and memory core to try to understand how an away team beamed back with a light virus from Hetemit IX. He bemoaned it was likely to take all night to complete. ()

In 2266, Scotty ran a level 5 diagnostic of the USS Enterprises transporter console just before beaming up Captain Kirk from planet Alfa 177. ()

Level 10 diagnostic  
In 3189, after the  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. ()

Other
Security diagnostic ()
Complete systems diagnostics ()
Transtator assembly diagnostic ()

Appendices

See also
Diagnosis
Diagnostic and Repair Technician, Junior Grade
Diagnostic array
Diagnostic subroutine
Diagnostic team
Jupiter Station Diagnostic Program Alpha-11
Megalite survey
Self-diagnostic
Troubleshoot

Background information
From the entry "diagnostic" in the , "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)."

de:Diagnose
Computer technology
Scans