Oven displays F91 and the door lock status does not match the actual door position (e.g., shows locked when open).

Safety first: Turn off power at the breaker.

• Check door alignment: Verify that the door closes squarely and that the latch engages the frame evenly. Adjust hinges if the door is sagging.
• Inspect latch and strike: Ensure the latch hook is not bent and that screws are tight.
• Access lock switch: Remove the top or rear panel to reach the lock assembly. Observe how the switch is actuated when the lock moves.
• Test switch continuity: With a multimeter, check the switch operation while manually moving the lock. Replace the lock assembly if the switch does not change state reliably.
• Check wiring: Inspect the harness from the switch to the main PCB for damage or loose connections.

Note: Because the switch is integrated into the lock assembly on many LG Studio models, replacing the entire assembly is often the most practical repair.