The thing I learned when I had dishwasher issues was to always start with the manual. You’ll probably be surprised with how much info is in the manual.

The Samsung dishwasher I had issues with had 50+ pages worth of diagnostics and repair instructions, including detailed meanings for every unique error code that can occur, and instructions for putting the whole unit into a test mode, where you can force each motor to run independently, run test routines for sensors, etc. Gave me everything I could want for DIY repairs.

Can’t say it’s always this nice, of course, but this adivce has served me well for other appliances since.