Microwave displays E4 and will not start; sometimes appears immediately after pressing START.

Safety first: Unplug the microwave before any disassembly. The door interlock system is a critical safety feature that prevents microwave radiation leakage.

Basic door checks:

• Open and close the door firmly several times. Listen for distinct clicks from the internal switches.
• Inspect the door latch hooks on the door for cracks, looseness, or misalignment.
• Check that the door closes evenly and is not sagging on one side.

Interlock switch inspection (qualified DIYers):

• Remove the outer cabinet to access the door interlock switch assembly near the latch area.
• Identify the primary, secondary, and monitor switches mounted on the interlock bracket.
• Visually inspect for burnt terminals, loose connectors, or broken plastic mounts.
• With a multimeter, test each switch for proper open/closed operation as the door is opened and closed (follow the service manual sequence).

Repairs:

• Replace any door switch that does not change state correctly or shows signs of overheating.
• If the plastic interlock bracket is cracked or loose, replace the bracket to ensure proper switch alignment.
• Do not alter wiring or bypass the monitor switch; this is a serious safety hazard.

When to call a technician: If you are unsure about switch wiring or alignment, have a professional perform the repair and leakage test.