I wish I had an error code but when it faults out it just gives a non-stop steady blinking LED. No variation that would indicated an error code.
Multimeters can be used to simply find out if a part is working. I recently used it when I lost hot water. By reading the voltage of the flow sensor, it was clear that the flow sensor bad (water running should give voltage X and still water should give voltage Y). I’m not sure how many such opportunities there are with washing machines though.
I really wish I could buy a new model control panel and put it on an old model so I can get useable diagnostics. (maybe I can?) Really hard to accept there is a water supply issue. It fills fine and it knows when to stop filling. The pump is fine, and also clear when I drain it and examine behind the drain plug. Surely if there were a water supply issue it would not fill the tub then decide after filling the tub and making some a few short fast spins that there is a water supply issue. I’ll pull out the water filter and see if anything looks sketchy. But I somewhat suspect the speed controller since the tumble (wash) cycle is way too fast.