the self-cleaning mop pad feature on the dock isn't working, the pads still look dirty and smell bad after washing

Diagnosis

The failure of the Dreame L40 Ultra to properly clean its mop pads usually stems from a breakdown in the hydraulic cycle within the base station. If the pads remain dirty, the "wash-plate" (the tray where the robot sits) is likely accumulating a layer of sludge, hair, and debris that prevents the cleaning solution from reaching the pads effectively. When the water cannot flow freely across the plate or the suction cannot pull the dirty water away fast enough, the pads are essentially being scrubbed with contaminated water, leading to that persistent "sour" smell. Furthermore, the smell is typically a result of biological growth (mold or mildew) occurring in the dirty water tank or the internal drainage pipes. If the dirty water tank isn't emptied immediately or if the drying cycle is interrupted, moisture traps bacteria in the fabric of the pads and the crevices of the dock. You can confirm this by inspecting the bottom of the mop pads; if there are brown streaks or a slimy residue despite the wash cycle, the issue is a combination of a clogged wash-plate and insufficient suction during the drainage phase.

How to Fix It

To restore the cleaning efficiency of your L40 Ultra, follow this deep-cleaning sequence:

1. Remove the mop pads from the robot manually. Take them to a sink and hand-wash them with a mild detergent until the water runs clear. Wring them out completely.
2. Remove the dirty water tank and the clean water tank. Use a bottle brush to scrub the interior walls of the dirty water tank, paying close attention to the rubber seal and the float sensor.
3. Locate the wash-plate (the removable tray at the bottom of the dock). Lift it out and use a damp cloth or an old toothbrush to scrub away the accumulated grime and hair from the drainage holes. If the holes are blocked, the water will pool and leave the pads dirty.
4. Clean the filter mesh located at the base of the dirty water tank intake. If this mesh is clogged with lint, the dock cannot suction the wash water away, leaving the pads soaking in filth.
5. Reinstall everything and navigate to the Dreamehome App. Go to Settings > Maintenance > Mop Cleaning. Change the "Mop Washing Frequency" to "Deep" and ensure the "Hot Water Wash" toggle is enabled.
6. Run a manual "Self-Cleaning" cycle from the app while the robot is docked to flush the internal plumbing.
7. Ensure the "Hot Air Drying" is set to at least 3 hours to completely eliminate the smell.

If That Didn't Work

• Check the Water Supply: Ensure the clean water tank is fully seated. If there is an air lock in the pump, the dock won't dispense enough water to saturate the pads. Try filling the tank with warm water (not boiling) to help break down existing residue in the internal lines.
• Inspect the Drain Valve: Check the rubber gasket at the bottom of the dirty water tank. If the seal is warped or has a piece of debris trapped in it, the vacuum pump will leak air and fail to create the suction needed to pull dirty water off the mop pads.
• Use a Specialized Cleaning Solution: If the smell persists, add 10ml of the official Dreame cleaning solution to the clean water tank. Avoid using bleach or thick detergents, as these can foam over and damage the internal pump sensors.
• Hard Reset the Dock: Power down the dock by unplugging it for 60 seconds. This can sometimes reset the pump logic if the system was experiencing a "dry run" error that prevented the full wash cycle from completing.

Heads Up

• Empty the Tank Immediately: Never leave dirty water in the tank for more than 24 hours. The L40 Ultra's tank is airtight, which creates a breeding ground for anaerobic bacteria and the subsequent "sour" smell.
• Avoid Thick Detergents: Only use low-sudsing cleaners. High-foam soaps will trigger the overflow sensor and cause the dock to stop the washing process prematurely.
• Weekly Plate Maintenance: Make it a habit to remove the wash-plate once a week and rinse it under a tap; the "self-cleaning" feature of the dock cannot remove hair clumps or thick mud.
• Dry Cycle Priority: Always ensure the robot has enough battery to complete the full drying cycle. If the robot is interrupted during drying, the damp pads will develop mold within hours.