Microwave displays E4 and will not start any cooking program

Safety first: Unplug the microwave before removing any covers. Avoid contact with high-voltage components.

Step-by-step checks:

• 1. Clean the cavity: Wipe the interior, especially the area near the top or side where the humidity sensor window is located (often behind a small grille). Use a mild detergent and soft cloth to remove grease and food residue. Dry thoroughly.
• 2. Power reset: After cleaning, leave the door open and allow the cavity to dry. Then plug the unit back in and check if the E4 code clears.
• 3. Access humidity sensor (for experienced users): Remove the outer cabinet. Locate the humidity/steam sensor module, usually near the top of the cavity with a small opening into the cooking chamber. Inspect the wiring harness for loose or damaged connectors. Reseat the connector firmly.
• 4. Sensor test: If you have the Daewoo service manual, follow the specified resistance or voltage checks for the humidity sensor. Replace the sensor if readings are out of range.
• 5. Control board inspection: If the sensor and wiring are good, the fault may be on the control PCB. Look for burnt components or corrosion. Control board replacement is typically a technician job.

Note: Do not operate the microwave with covers removed. If E4 persists after cleaning and reseating connectors, professional service is recommended.