Robot mower shows E20 and stops when encountering obstacles, even small ones.

Safety first: Turn off the mower before cleaning or adjusting any sensors.

• Clean sensor faces: If your AL-KO model has ultrasonic sensors on the front, gently clean them with a soft, damp cloth to remove dirt, grass, or insect residue.
• Check alignment: Ensure the sensor housings are not pushed in or tilted from impacts. Realign or reseat them in their mounts.
• Inspect wiring: Remove the front cover and check the harness from the sensors to the main PCB. Look for pinched or broken wires and reseat connectors.
• Test in open area: Place the mower in an open, obstacle-free area and start a test run. If E20 still appears, the sensor module may be defective.
• Module replacement: Replace the ultrasonic sensor module with an original AL-KO part if cleaning and wiring checks do not resolve the issue.