SubZero Refrigerator Freezer Error Code 90 H 84 – How to fix? by KatyApplianceRepair.com 

Sub-Zero error code EC 90 H 84 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 H 84	Communication fault — variant of EC 90 series indicating board communication failure	High

Cause & Solution

Cause	What to Check	Fix
Communication cable fault	Inspect and re-seat all board-to-board cables	Replace damaged cables; reset the unit
Faulty control board	If cables are intact, board diagnostics are required	Replace the control board — certified technician recommended