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Parts for GE GHDA450L00BB Dishwasher - AppliancePartsPros.com

If you click on a part's picture or description then a new page will open often with how to remove it in the Q&A section.
For instance gently pull up while turning the spay arm counterclockwise to remove it.

First I would check if the unit is filling correctly.
Most units fill to just under the heating element.
The Q&A says this unit should fill 1/3 to 1/2 up the float assembly cover.
You can check this by opening the unit up after a fill and adding a gallon or so of hot water to the unit.
Just be careful that you do not overfill it.

If it now works OK the most likely cause is a partially plugged screen filter on the input side of the fill valve.
Remove the fill valve and check/clean the screen.
Do not permanently remove it as it is there to keep crud out of the valve which could hold it open and cause a flood.

If the screen is clean I would replace the valve.