The Automatic Test Mode scans through all of the pin connections. First, it determines the connectors used. Second, it checks for several types of "fatal errors"; no cable connected, more than one cable connected, shorts between power and other pins, a plus voltage connection without a corresponding ground, etc. If any of these faults are found, a "Bad Cable" page is displayed, with the fault(s) explained.
If the cable passes all of the tests, the tester then creates a numeric "map" of all the cable pin connections. It then looks at files on an internal SD memory card to find a matching "map" in a specific cable definition. When a match is found, a list of possible cable part numbers is displayed, along with some other test results.
If everything is good, the info listed above is shown on a "Good Cable" screen. However, there are cable definitions on the SD card for some common wiring mistakes and shorts. In this way, a cable match can be found and displayed on a "Bad Cable" screen for cables that are damaged or wired incorrectly.
In addition to the Automatic Test Mode, there is a Manual Test Mode, which steps through the pins and lights LEDs on the console. This allows the operator to wiggle the connectors, and identify intermittent problems, when the LEDs flicker.