Possible Causes

Failed evaporator temperature sensor, Broken or iced-over sensor connection, Main control board not reading defrost sensor

How to Fix / Troubleshooting

Safety first: Unplug the refrigerator. Be cautious of sharp evaporator fins and avoid using metal tools on ice.

Steps to check:

Access the evaporator: Remove shelves and the rear panel in the affected compartment (often the freezer). You may need to defrost heavy ice with a hair dryer on low, keeping it away from plastic parts.
Locate the defrost/evaporator sensor: It is typically clipped to the evaporator tubing or mounted near the top of the coil.
Inspect and test: Check for broken wires or a sensor that has come loose from the coil. Test resistance with a multimeter and compare to the Thermador NTC chart. Replace if out of spec.
Secure the new sensor: Clip or tape the new sensor firmly to the evaporator line in the same position as the original to ensure accurate readings.

Note: If the sensor is good and E05 persists, the main control board's defrost circuit may be faulty and require professional replacement.