There are 5 main levels of diagnostics:

Level 5 Diagnostic

This automated procedure is intended for routing use to verify system performance. Level 5 Diagnostics, which usually require less then 2.5 seconds, are typically performed on most systems on at least a daily basis, and are also performed during crisis situations when time and system resources are carefully managed.

Level 4 Diagnostic

This automated procedure is intended for use whenever trouble is suspected with a given system. This protocol is similar to Level 5, but invokes more sophisticated batteries of automated diagnostics. For more systems, Level 4 diagnostics can be performed in under 30 seconds.

Level 3 Diagnostic

This protocol is similar to level 1 and 2 diagnostics but involves crew verification of only key mechanics and systems readings. Level 3 diagnostics are intended to be performed in ten minutes or less.

Level 2 Diagnostic

This refers to a comprehensive system diagnostic protocol which, like a level 1, involves extensive automated routines, but requires crew verification of fewer operations elements. This yields a somewhat less reliable system analysis, but is a procedure that can be conducted in less then half the time of the more complex tests.

Level 1 Diagnostic

This refers to the most comprehensive type of system diagnostic, which is normally conducted on ship systems. Extensive automated diagnostic routines are performed, but a level 1 diagnostic requires a team of crew members to physically verify operation of a system mechanisms and to take system readings, rather then depending on the automated programs, thereby guarding against possible malfunctions in self testing hardware and software. Level 1 diagnostics on major systems can take several hours, and in many cases the subject system must be taken offline for all tests to be performed.