Take a look at the solenoid valve on the pump.
It should be up (released).
It controls the water flow.
So up is flow to the wash arms.
Down is flow to the drain.
The way it works is that during fill and wash cycles the solenoid is up so the water flows to the wash arms.
When it is supposed to drain power is applied to the solenoid for a couple seconds, pulling it down.
The water is then directed out the drain. The water pressure keeps the flapper/solenoid in this position, once the water is drained the springs pull the solenoid back to the up position.
There are problems with the solenoid getting power for too long.
This is often timer contacts sticking closed.
It then overheats and his melts plastic in the solenoid causing it to stick in one position.
So also check that it moves up and down fairly easily.