Robot vacuum reports E4 and stops, usually near stairs or dark carpets; voice prompt may mention cliff sensor or anti-drop error.

Safety first: Turn off the robot and place it on a table or counter with a soft cloth underneath.

• Locate cliff sensors: On most Neabot robots, cliff sensors are on the underside near the front edge, in small recessed windows.
• Clean sensor windows: Use a dry microfiber cloth or cotton swab to gently wipe each sensor window. If there is sticky residue, lightly dampen the cloth with water (not alcohol) and wipe, then dry immediately.
• Check for physical damage: Inspect the sensor windows for cracks or deep scratches. If the plastic is opaque or cracked, the sensor assembly may need replacement.
• Test on light surface: Place the robot on a light-colored, flat floor away from stairs and dark rugs. Power it on and start a cleaning cycle.
• Reset environment: Avoid direct sunlight shining under the robot; strong IR light can confuse cliff sensors. Close blinds or move to a shaded area.

Warning: Do not cover cliff sensors with tape or stickers to bypass the error; this can cause the robot to fall down stairs and be damaged.