GE Dishwasher GSD5500G01BB Standing water (abt an inch or more) left after draining. I cleaned the filter. It appears to drain fine just not all the way. I can see the water being pumped out to the drain pipe. When I put it in F1 Test Mode and run it through the cycle it will drain all the way. Ideas?

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Replacement parts for General Electric GSD5500G01BB Dishwasher | AppliancePartsPros.com

Probably drains better in test mode just because the drain time is longer.

Your unit has a piston & nut (see 564 in Section 1). This is a common cause of drain problems.

If it does not seal properly during a drain cycle some water is directed back into the tub instead of out the drain.

It is under the screen cover at the back of the tub and it unscrews.
Remove and check it.