Diagnosis
The infrared 'Ice Full' sensor lens is either dirty or blocked, so it can't detect the ice level.
How to Fix It
Unplug. Open the lid and look at the left-side interior wall—you'll see a small, clear plastic window (the sensor). Clean it meticulously with a cotton swab dipped in rubbing alcohol. Also, ensure the corresponding sensor on the opposite wall is clean.
If That Didn't Work
The sensor may be misaligned due to the basket not being seated correctly. Remove the ice basket completely and check its shape—if it's warmed from hot water cleaning, it might not sit at the right height. Ensure it clicks firmly into the guides.
Heads Up
Don't stack ice above the MAX line even if the light isn't on. The sensor isn't perfect, and overflow can cause water to leak into the electronics below.