The diagnostic test will only tell you a component is funstion. Not functioning correctly.
For extended was times and poor cleaning,check the following;
Clean filter.
Full water level.
Drain loop is high.
All wash arms rotating.
Water temp at 140 plus.
Correct detergent.
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A dirty water filter will result in slow dirty water movement.
A too low water level results in not enough water to do a good job.
A poor drain loop allows dirty sink/disposal water to enter the machine.
A stuck or poorly rotating wash arm could be caused by a bad wash pump impeller.
Could also be caused by a warped wash arm hanging up.
Less than 140 degree wash water could be a defect in the heating circuit resulting in extended wash cycles.
Too much or wrong detergent could result in sudsing or other poor wash conditions.