Robot mower shows E4 and will not start mowing; error appears immediately after pressing START.

Safety first: Turn the main power switch OFF and remove the battery if possible. Wear cut‑resistant gloves. Never work near the blades with power ON.

• Inspect the cutting disc: Turn the mower upside down on a soft surface. Check for grass, string, or wire wrapped around the blade disc or motor shaft. Remove all debris carefully.
• Check for foreign objects: Look for stones, branches, or toys lodged under the deck that could block the disc. Remove them and inspect the deck for damage.
• Spin the disc by hand: The disc should rotate freely with slight resistance. If it feels rough, seized, or wobbly, the Blade Motor Assembly or its bearings may be failing.
• Check blades: Ensure the small pivoting blades are not bent into the deck. Replace damaged blades and screws with genuine Kress blades.
• Reset and test: Turn power ON, clear the error, and start a short test. If E4 returns immediately with a free‑spinning disc, the motor windings or current sensing circuit on the Main Control Board may be defective and require professional service.