SubZero Refrigerator Freezer Error Code 90 5 80- How to fix? by KatyApplianceRepair.com 

Sub-Zero error code EC 90 5 80 indicates
a main-board communication issue. Below is a quick reference
and troubleshooting guide for this code.

Quick Reference

Error Code	Meaning	Severity
EC 90 5 80	Communication fault between the display board and main control board	High

Cause & Solution

Cause	What to Check	Fix
Loose or corroded ribbon cable between boards	Inspect the communication cable between the display and main board	Re-seat the cable; clean connector pins with contact cleaner
Faulty main control board	If cable is secure, test board outputs	Replace the main control board