Diagnosis
The infrared sensor that detects a full basket is either blocked, dirty, or has failed. It's a small window inside the unit, usually near the ice chute.
How to Fix It
Power off and unplug. Remove the ice basket. Look for a small plastic lens (often clear or red) on the side wall of the ice compartment. Wipe it perfectly clean with a soft, dry microfiber cloth—any dust or water spots can block the signal. Also, check that the corresponding sensor on the basket itself (if present) is clean. Plug back in and test.
If That Didn't Work
The sensor is misaligned or broken. Manually trigger it: with the unit on and empty, use your finger to gently cover the sensor lens. The 'full' light should illuminate immediately. If it doesn't, the sensor circuit is dead. Your only workaround is to manually monitor the basket and press Stop before it overflows.
Heads Up
Overfilling can damage the ejector mechanism as ice jams in the chute. Never leave it running unattended for hours until you've verified the full sensor is working. Stacking ice too high above the sensor line will also defeat it.