Diagnosis
F7E1 is a communication error between the main control board and the user interface (UI) board. The two boards aren't talking, so the machine faults. This can happen after a power surge or as either board starts to fail.
How to Fix It
First, try a hard reset. Turn off the circuit breaker to the dishwasher for 2 minutes, then turn it back on. Often, this reboots the system and clears the error. If the code returns immediately, the UI board (W10889179) is the most likely culprit and needs replacement.
If That Didn't Work
If a new UI board doesn't fix it, the main control board (W10878637) is probably the source of the failure. Replacing that is a bigger job, as it's mounted behind the kickplate at the bottom front of the tub.
Heads Up
There's a small chance it's just a loose ribbon cable connection between the boards. Before buying parts, you can (with power OFF) open the door panel and check that the cable is firmly seated. But in my experience, it's usually a board failure.