Here is the parts breakdown
Model SearchAs applianceman said low water can cause this.
If you have a low water condition you usually will hear a growling sort of sounds as the pump sucks in air and cavitates.
Normal water level is just under the heater element.
Remove the kick plate and take a look underneath, make sure the wash/drain solenoid (left hand side of the pump) is returning all the way up to home/wash position.
Remove the lower wash arm and check it.
Check the area under it for debris.
Check that Item 545 is not badly worn. Note they have changed the design in this area so if it is shot you have to get a kit. They are usually OK.
Also check the little flapper valve. Item 557 in the "Motor pump mechanism" section. It allows water to drain back into the pump during drain but should close when in wash. If it does not close you loose a lot of pressure out of the hole instead of it going up to the spray arms. They rot out over time.
Take a look down in this area so you can see the wash/drain flapper valve many of them have a rubber seal in the center, make sure that you do not have just a hole.
Remove the sump cover and check the sump for debris. Also check that the chopper wire does not have a twist tie etc. wrapped around it. Make note of how the inner grate goes on. Put it back the wrong way and the chopper will eat it.
Since you are in there you may as well also check your piston and nut, Item 564 in the "Body parts" section. It is under the cover with the screen at the back of the tub. This usually shows up as a poor drain problem but is a part which fails often so is worth a look.
Might as well also open up the float assembly (left hand front) in the tub and clean it. They get gummed up over time.
Note that some of the parts are left hand tread. Spray arm and piston/nut, but I am not sure.
There you have now cleaned check the water flow path of the unit and it should now be OK.
