Safety first: Switch OFF the mower and remove the battery before working on the bumper assembly.

Check bumper movement: Press the front bumper in at several points. It should move freely and spring back evenly. If it sticks, clean out grass and dirt from the bumper gap.
Inspect springs and guides: Remove the front cover to access the bumper mechanism. Check that springs are intact and guides are not cracked or bent.
Test microswitches (advanced): Locate the bumper switches and manually press them while listening for a click. Use a multimeter to verify continuity when pressed.
Check wiring: Follow the bumper harness back to the main PCB. Ensure connectors are secure and wires are not pinched.
Replace faulty parts: If a switch does not click or test correctly, replace the NAC bumper switch set or complete bumper sensor assembly.

Warning: Do not operate the mower with the bumper disabled; collision detection is essential for safe operation.

Robot lawnmower shows E10 Sensor Error; mower behaves erratically near boundary and obstacles.

Possible Causes