Diagnosis
A misaligned or faulty door switch is telling the control board the door is open. The primary suspect is the refrigerator (fresh food) door switch.
How to Fix It
Test and replace the faulty door switch. Unplug the refrigerator. Remove the top hinge cover and then the door's inner liner cap to access the switch wiring. Use a multimeter to test for continuity when the switch plunger is depressed. No continuity means a bad switch. Replace it (Part # WR55X10025).
If That Didn't Work
The door may be out of alignment, preventing the plunger from being fully depressed. Loosen the hinge screws, realign the door so it sits flush, and retighten.
Heads Up
You can temporarily silence the alarm by holding the "Alarm/Reset" button on the display panel for 3 seconds. This is a temporary override, not a fix.