Refrigerator shows E4 and may not defrost properly, with frost buildup on the freezer back wall.

Safety first: Unplug the refrigerator before accessing the freezer evaporator area.

Inspection:

• Remove freezer drawers and the rear panel to expose the evaporator coil.
• Locate the defrost sensor/thermistor clipped to the evaporator tubing.
• Check that it is firmly attached to the coil and that the wires are not cut or pinched.

Testing:

• Disconnect the sensor and measure resistance at a known temperature (often around 10k ohms at 25°C, but verify model-specific values).
• If the sensor reads open, shorted, or far off spec, replace it.

After replacement: Reassemble the evaporator cover, restore power, and allow 24 hours for normal frost pattern to return. If E4 persists with a known-good sensor and wiring, the main control board may require replacement.