Robot vacuum reports C9 and stops; may say 'Please check the anti-drop sensors' or 'Please move the robot to a new location'.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Strong sunlight or reflective floor confusing sensors, Dirty cliff sensors, Internal sensor calibration drift, Main board sensor input fault

Safety first: Turn the robot OFF.

Move to a different area: Place the robot on a non-reflective, matte floor away from direct sunlight or mirrors.
Clean cliff sensors: Wipe all underside cliff sensor windows with a soft cloth.
Power cycle: Turn the robot OFF for 30 seconds, then ON, and start a cleaning cycle.
Check firmware: Use the Ecovacs app to check for firmware updates, as some models improve sensor handling via updates.

If C9 persists in all environments: The cliff sensor board or main control board may be faulty and require replacement.

Hard 4/5

Cliff Sensor Board or Main Control Board

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