Top rack dishes are not getting clean while bottom rack appears fine.

Safety first: Turn off power before removing internal components.

• Clean upper spray arm: Remove the upper spray arm and flush out debris from all jets.
• Inspect feed tube: Check the vertical feed tube and manifold for cracks or disconnections. Ensure it engages properly with the rear wall port when the rack is pushed in.
• Check diverter function: If your Viking model uses a diverter, verify that water is being directed to the upper rack during part of the cycle. Replace the diverter if it fails to switch.