Whirlpool DU1055XTSS Quiet Partner 1 is not cleaning top rack

Make sure the center loading is not obstructing the water jet to the top shelf. Top shelf is only for glasses and saucers , use Jet-Dry .Pre rinse and clean bottom pan strainer from dirt debris.

if it is just affecting the upper rack i doubt it is just a plugged spray arm (though i could be wrong). more likely than not you have a blockage on the intake of your spray pump motor. a series of bones, toothpicks, foreign material, etc could be blocking the entrance of the pump causing it to starve for water so to speak.
you will more than likely need to remove the lower rack and spray arm to be able to disassemble the strainer and gain access to the sump.
a complete model number would help bunches to.. alas

Hi,

I would suspect you have debris in the pump that is causing a pressure drop so the water is not spraying well in the upper arm.

Try this procedure to clean out the sump. Let me know if it helps.

http://www.fixya.com/support/r4628450-poor_cleaning_or_noisy_pump_whirlpool_or

two things that you need to check one is the water level in the machine when it has completed it fill cycle.low water level will cause this issue with imporper cleaning.
make sure the spray arm is not clogged in any way.
the other is simply replace the main wash motor

I have same problem, anybody know how to fix this?

check the choper assembly

In my experience, you probably have a clog in the spray arm/arms for the top rack. Take the arm(s) out and see if the holes in them are clogged. Rice, plastic wrappers, and glass from dishes that broke in there are the most common culprits I've seen.

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First, confirm that the holes are not blocked on these arms. (I did not want to assume you have done this.)

Then check the impeller on top of the motor stem for being loose or worn/damaged - to rule the impeller out. If it is fine, then the motor is failing and too weak to drive the spray arms.
To answer your question, I think the answer is "They don't make them like they used too!"

Have this same problem with my Whirlpool DU1145XTBA. Found out that when you start the unit, it fills with water. If the water does not rise above the filter mesh in the bottom center of the unit then the pump doesn't have enough water to supply pressure to the upper sprayer. Had to replace the Flow Meter. It tells the unit how much water to supply to the unit.