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Replacement parts for General Electric GSD5500G03WW Dishwasher | AppliancePartsPros.com

If the unit is also not washing correctly, check for debris etc. in the sump, center of tub.
Be careful there is often broken glass in the sump.
Also take note of how the insert is installed, replace it incorrectly and the chopper will eat it.

Check that the drain line is clear.
Check that it is still looped up high that the drain, sometimes they can come loose, drop down and siphon water back into the unit.
A common spot for it to clog is where it attaches to the house plumbing.
You could unhook it and try draining it into a pail. Just be sure to hold the drain line securely and put a towel over it so it does not splash all over.

A common problem with these units is a leaking Piston & Nut valve, Item 564 in Section 2.
It is under the screen filter at the back of the tub. It unscrews.
If it does not seal correctly some water is diverted back into the tub when draining instead of it all going out the drain.
If the seal on it is shot replace it.

After that I would check the drain pump

Note: The Piston and Nut should be at the top of the list. They often fail.

[COLOR="Blue"]Do I have to remove the dishwasher to get at these parts?[/COLOR]
No, you should be able to get to all of them from inside the tub, just remove the lower rack.
Only the drain pump is under the unit and may require removing the unit.

[COLOR="Blue"]Also is there some kind of step by step to get to these parts??[/COLOR]
Not really. Undo the bolts, remove the covers. It is rather self evident.
The drain pump is harder but do the others first.
It may also be the flapper valve near the pump depending on how it is hooked up/