Robot mower stops and displays E004 when trying to drive; wheels do not turn.

Safety first: Turn OFF the main power switch and keep the mower on a stable surface.

• Inspect drive wheels: Check both left and right drive wheels for wrapped grass, roots, or string. Remove any obstructions carefully.
• Check wheel rotation: Lift each side of the mower and rotate the wheel by hand. It should turn smoothly with some gearbox resistance but no grinding or locking.
• Inspect wheel treads: Look for stones or hard objects lodged in the tread that could jam the wheel.
• Check underbody: Ensure no branches or edging stones are wedged under the chassis preventing movement.
• Test again: Turn power ON, clear the error, and command a short manual move. Listen for abnormal grinding or clicking from the gearbox.

Persistent E004 with free-spinning wheels suggests a failing drive motor, gearbox, or motor driver circuit. These typically require replacement of the affected drive motor assembly.