I had this exact issue — the upper spray arm stops spinning, dishes stay dirty, and soap pods barely dissolve. Even after cleaning everything, nothing improves. That usually means water isn’t reaching the top properly.
Quick Answer
If the top arm isn’t spinning and detergent isn’t dissolving, the problem is usually low water pressure inside the dishwasher, caused by a faulty circulation pump, arm selector motor, or blockage in the feed system.
Step-by-step troubleshooting guide
1. Confirm the main symptom (important clue)
You’ve already noticed:
- Upper arm not spinning
- Pods not dissolving
👉 This strongly points to weak or no spray pressure, not just a clogged arm.
2. Check water level inside the dishwasher
Even though you added water manually, confirm:
- Start a cycle
- Open after fill
- Water should sit just below the heating element
If low:
- Could be a faulty inlet valve
3. Test the circulation pump (most likely issue)
The circulation pump drives all spray arms.
Signs it’s failing:
- Weak water movement
- Arms not spinning
- Pods not dissolving
Quick test:
- Start a wash cycle
- Listen for a strong spraying sound
If it sounds weak or quiet → pump issue likely.
4. Check the spray arm feed tube
Water reaches the top arm through a vertical channel.
- Inspect the rear feed tube
- Make sure it aligns properly with the rack
- Look for cracks or blockages
If misaligned, water won’t reach the upper arm.
5. Inspect the arm selector motor (very common on Bosch)
This matches the answer you found.
Bosch dishwashers use a diverter (arm selector motor) to switch water between arms.
If faulty:
- Water may only go to the bottom arm
- Upper arm stays still
What to check:
- Wiring connections
- Signs of damage
- Whether it’s stuck in one position
6. Check the impeller (your current suspicion)
You can test it before replacing:
- Remove lower components
- Spin the impeller manually
- It should move smoothly
If damaged:
- Blades may be worn
- Pump can’t generate pressure
👉 Your order for this part makes sense if pump pressure is weak.
7. Run a simple spin test
Quick real-world test:
- Place a small object (like a toothpick) on the upper arm
- Run a short cycle
- Open after a minute
If it hasn’t moved → no water reaching it.
8. Access diagnostic mode (if available)
Bosch models like SHE68R55UC don’t always label buttons clearly.
Typical method:
- Turn dishwasher off
- Press and hold two program buttons
- Turn power on
(Exact combo varies, but usually the two leftmost buttons)
This can:
- Show error codes
- Run test cycles
Extra tips and best practices
- Always clean filters regularly
- Ensure racks are seated properly (alignment matters)
- Use proper detergent and avoid overloading
- Run hot water at the sink before starting a cycle
Common mistakes to avoid
- Replacing the impeller without checking the diverter motor
- Ignoring weak pump sounds
- Assuming clogs are the only issue
- Misaligning the upper rack feed tube
FAQ
Why is only the top rack dirty?
Because water isn’t reaching the upper spray arm, usually due to pump or diverter issues.
Can a bad impeller cause this?
Yes. A worn impeller reduces pressure, affecting all spray arms.
Is the arm selector motor a common failure?
Yes. On many Bosch models, it’s a frequent cause of uneven washing.
Conclusion
From your symptoms and what you’ve already tested, the most likely causes are:
- Weak circulation pump or damaged impeller
- Faulty arm selector (diverter motor)
Since you’ve cleaned everything and even added water, focus on water pressure components, not blockages. Testing the pump and diverter will point you to the exact fix.
Reference links
https://www.bosch-home.com/us/owner-support/get-support/dishwashers
https://www.repairclinic.com/RepairHelp/How-To-Fix-A-Dishwasher/33-4--/Dishwasher-Not-Cleaning-Dishes
https://www.appliancepartspros.com/repair-help/dishwasher-repair-help/dishwasher-spray-arm-not-spinning.html
