Microwave beeps and displays E4; unit will not start a cooking cycle.

Safety first: Unplug the microwave before removing any panels.

Cleaning and inspection:

• Clean the cavity: Food splatter and grease can coat the humidity sensor. Thoroughly clean the interior with a mild detergent and warm water, especially near the top or side wall where the sensor window is located. Dry completely.
• Locate the humidity sensor: On many Emerson models, the sensor is a small component behind a grill or opening in the upper cavity wall or ceiling. Remove the outer cabinet to access the sensor from the top or side.
• Check connections: Ensure the sensor’s wiring harness is firmly seated in both the sensor and control board connectors. Look for corrosion or damaged wires.
• Test the sensor (if equipped to do so): Using a multimeter, compare resistance readings to the service manual specifications. If readings are out of range or open, replace the sensor.

Reset and test: After cleaning and reseating connections, reassemble the unit, plug it in, and clear the error by unplugging for 5 minutes. Test an auto-cook or sensor-cook function to see if E4 reappears.

Note: If the error persists after sensor replacement, the control board’s sensor circuit may be defective and require professional replacement.