Diagnostic mode is a 3-5 minute cycle you or anyone can run on your washer that will check the washer for any issues or errors.
If any are found it will report them back to you using a series of blinking lights that you have to decode using a manual that's found hidden inside your washer.
Recalibration mode is a basically a factory reset for a washer, another thing it does is check itself for any issues and If any are found it will give you a blinking light code that explains the issue. Recalibration is recommended after moving, installing or repairing the washer
PRO TIP:
Sometimes simply running recalibration mode fixes the washer. Learn how by clicking the get started button bellow