4 SY Moderate Moderate DIY

Frigidaire Refrigerator 4 SY — Ambient / Defrost Sensor Open

Frigidaire Refrigerator · Error code 4 SY

What 4 SY Means

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

Symptoms

  • 4 SY displayed
  • Defrost timing off
  • Frost or temperature drift
  • Energy use higher than normal

Common Causes

1
Open ambient thermistor

Sensor element failed.

2
Broken wiring

Conductor severed.

3
Disconnected harness

Pin not seated.

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.

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.

Common replacement Ambient/defrost thermistor View on 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 — Evaporator Sensor Shorted 3 SY 3 SY — Evaporator Sensor Open

All Frigidaire codes → All refrigerator codes →

Verified against manufacturer documentation: frigidaire.com

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.