From Bravo Fleet Infobase
Star Ships and Stations are a collection of complected systems. To keep those systems at the highest level operational readiness preprogrammed diagnostic software and procedures for use in the event of actual or possible malfunctions. The various diagnostic protocols are generally classified into five different levels. Which type of diagnostic is used in any given situation will generally depend on the situation and time allotted for the diagnostic procedures.
Level 1 Diagnostic:
This refers to the most comprehensive type of system diagnostic. Extensive automated diagnostic routines are performed. A team of crew members are to physically verify operations of system mechanisms and system readings. Guarding against possible malfunctions in self-testing hardware and software. A level 1 diagnostic of major systems can take several hours and in many cases the subject system must be taken off-line of all tests to be performed
Level 2 Diagnostic:
This refers to most comprehensive type of system diagnostic. Extensive automated diagnostic routines are performed. A team of crew members are to physically verify of fewer operational elements. For most systems, this can be performed in half the time of the level 1 diagnostic but will yield a somewhat less reliable system analysis.
Level 3 Diagnostic:
Extensive automated diagnostic routines are performed but only requires crew verification of only key mechanics and system readings. Level three diagnostics are intended to be performed in ten minutes or less
Level 4 Diagnostic:
This automated procedure is intended for use whenever trouble is suspected within a given system. The Level 4 diagnostic is similar to a level 5 diagnostic but involves more sophisticated batteries of automated diagnostics. The level 4 diagnostics are designed to be completed in under 30 seconds.
Level 5 Diagnostic:
This automated procedure is intended for routine use to verify system performance. Level 5 diagnostics usually require less than 2.5 seconds. Level 5 diagnostics are performed on all systems at least once a day and during crisis situations when time and system resources are carefully managed.