Display shows E4 and the freezer may not defrost properly, leading to ice buildup on the rear wall.

Safety: Disconnect mains power before accessing the freezer evaporator area.

• Defrost the freezer: Remove all food and drawers. Unplug the appliance and leave the door open until all ice on the rear panel has melted. Use towels to collect water; do not use sharp tools to chip ice.
• Remove rear freezer panel: Unscrew and carefully pull off the inner rear panel to expose the evaporator coil.
• Locate the evaporator sensor: Find the small NTC sensor clipped to the evaporator tubing or in a plastic holder.
• Inspect sensor and wiring: Check that the sensor is firmly attached and not corroded. Follow the cable to the cabinet pass-through and look for damage.
• Test sensor resistance: With the fridge unplugged, disconnect the sensor at the nearest connector or at the PCB and measure resistance. Compare to expected NTC values at the current temperature. Replace if readings are abnormal.
• Install new sensor: Fit a Grundig freezer evaporator NTC sensor, clip it securely to the same location on the coil, and route the wiring as originally installed.
• Reassemble and power on: Refit the rear panel, ensuring no wires are pinched. Restore power and monitor for proper defrosting and clearance of the E4 code.

Persistent E4 after sensor replacement may indicate a faulty main control board or defrost control circuit, requiring professional service.