If there is I20 on the display, you have a draining issue.
However, the code may persist even if the machine is draining well. It happens when the pressure switch remains on and behaves as if water were still there.
Take the washer out of its cabinet and remove the right-hand side panel. Also, remove the front bottom cover, which is located beneath the door.
You will see a round object with a thin hose leading to it in the bottom left corner. That is the pressure switch.
Pull out the hose and blow it through. Thus you will clear the pressure chamber.
Reassemble the switch and run the cycle again: most likely, it will work well.
Other dishwasher error code: