Frigidaire · Refrigerator Moderate

4 SY — Ambient / Defrost Sensor Open

Open reading on the ambient or auxiliary defrost sensor (varies by model). Used for adaptive defrost timing.

Keep using it?
Yes, with caution
DIY difficulty
Moderate
Verified against
frigidaire.com ↗

How to fix it

  1. Unplug refrigerator.
  2. Locate ambient/aux defrost thermistor per tech sheet (often near machine compartment or fresh-food top).
  3. Ohm sensor and replace if open.
  4. Check wiring back to main board.
  5. Replace main board if input is dead.

Why it happens

Typical signs: 4 SY displayed · Defrost timing off · Frost or temperature drift · Energy use higher than normal

  • Open ambient thermistor Sensor element failed.
  • Broken wiring Conductor severed.
  • Disconnected harness Pin not seated.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Ambient/defrost thermistor Common replacement
    Amazon →

More Frigidaire refrigerator codes

1F 1F — Ice Maker Fault 1 SH 1 SH — Fresh Food Sensor Shorted 1 SY 1 SY — Fresh Food Sensor Open 2 SH 2 SH — Freezer Sensor Shorted 3 SH 3 SH — Temperature Sensor Short 3 SY 3 SY — Evaporator Sensor Open

All Frigidaire codes → All refrigerator codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: frigidaire.com.