During start-up, a stand-alone Esc Esc D test, and during an ACABA subject test, the instrument runs a self-diagnostics sequence that includes a number of items listed at pages 71 through 73 of the 2013 Intoxilyzer 8000C Training Aid. These diagnostics do not check everything. Experimentally, you can disconnect many components and the instrument will still pass its Diagnostics test. The Training Aid says: "The Diagnostics check is a self-limiting evaluation of the functionality of the Intoxilyzer(c) 8000C. Nine different parameters are evaluated and each must successfully pass in order to operate the instrument. A successful Diagnostics check provides evidence to the breath technician that the instrument is operating properly." Lawyers need to learn the specific tests run during such diagnostics and more importantly what they do not check. Note that an Intoxilyzer may pass a Diagnostics test with no simulator/dry gas attached (although you will probably get an error during an Esc Esc C or ACABA sequence). Diagnostics check specific things at a particular point in time, not before or after that specific point in time. An instrument may fail start-up diagnostics 20 or 30 times, then start, and then run a successful diagnostic once electronic response/internal standards/ITPs have drifted close to where they should be. That doesn't make an otherwise unreliable machine reliable. See the video on the front page of www.impaired-driving.com.