Robot mower will not start mowing; display shows E01 immediately after power-on or when START is pressed.

Safety first: Turn the mower's main power switch OFF and remove the battery or disconnect the battery connector before opening any covers.

• Check the red STOP button: On most LawnMaster robot mowers the STOP button is on the top cover. Make sure it is fully released and not jammed. Press it firmly and then release it several times.
• Inspect for debris: Grass, mud, or small stones can wedge around the STOP button. Clean around the button with a soft brush and compressed air if available.
• Power cycle: Turn the main power switch OFF for 60 seconds, then ON again and check if E01 clears.
• Check the stop button wiring: Remove the top cover (usually several Torx screws). Locate the STOP button assembly and follow its two-wire harness to the main control board. Ensure the connector is fully seated and wires are not cut or pinched.
• Test the switch (advanced): With the battery disconnected, unplug the STOP switch connector and test continuity with a multimeter. The switch should change state (open/closed) when pressed and released. If it does not, replace the stop button assembly.

If the STOP button and wiring are good but E01 persists, the input circuit on the main control board may be faulty and the board will likely need replacement by a qualified technician.