In the book "A Guide to the Intoxilyzer 5000C", published by Amicus, the author, Amy Ramsay says at p. 43: "Diiferential Voltage Monitoring", the Instrument is displaying the microprocessor's output which allows the technician to check the signal's drift and stability. The DVM test is displayed only if a PROCESSOR ERROR 3, 4, or 5 occurs."
On an Intoxilyzer 8000C, the DVM monitor is accessed by an Esc Esc sequence at 2:D.