Safety first: Turn the robot OFF and place it upside down on a table or bench.

Check wheel movement: Manually rotate each drive wheel. They should turn smoothly with some resistance from the gearbox. If one is locked or very stiff, inspect closely.
Remove debris: Look around the wheel wells for hair, string, or carpet fibers wrapped around the wheel axle. Use tweezers or small scissors to remove all debris.
Inspect treads: Check the rubber treads for damage or objects wedged between tread and housing.
Power test: With the robot reassembled, place it on the floor and start a clean. Observe whether one wheel fails to turn or chatters before F4 appears.
Advanced check (for experienced users): If accessible, remove the wheel module screws and lift out the wheel assembly. Inspect the gearbox for broken gears or contamination. Replace the entire wheel module if damaged.

If F4 persists and one wheel does not drive, the wheel motor module should be replaced or serviced by a technician.

Robot displays F4 and will not move; may say there is a problem with the drive system or wheels.

Possible Causes