BI-36U Sub-Zero Refrigerator Door alarm

[gusz]

Model Number

BI-36U

Brand

Sub-Zero

Age

6-10 years

Sub-Zero Classic Series (BI) Displays dO Or​

My approx 10 year old Sub Zero Classic Series Model 36U over/under displays error message dO Or and door ajar alarm bell. With the door open the interior lights sometimes come on and sometimes not. I can clear the error at the button panel but it soon comes back.

The door switch seems to be operating correctly and I checked/cleared ice buildup in the freezer drawer. What else could cause this alarm?

Thx, Gus