LG microwave error codes: a sensor, a stuck key, or the lock.

The sensor that reads the air inside the cooking cavity is open or shorted, so the sensor-cook and auto settings cannot run.

1. Reset (unplug one minute) and run a cup of water for one minute on high.
2. If plain timed cooking works and only the sensor settings (Sensor Cook, Reheat, Popcorn) print the code, it is the sensor alone.

An F-1 that returns is the cavity sensor — a part inside the cabinet, a technician's job. Timed cooking still works meanwhile.

The control sees a key held down for longer than it allows.

1. Wipe the panel dry — grease from the range below and a wet rag both hold a key down.
2. Press each key once and feel for one that does not spring back.
3. Reset (unplug one minute).

A key that stays stuck after cleaning is the touch panel — a part, a technician's job.

Not a fault. The panel is locked so a child cannot start the microwave; the display reads Loc (or L, or the lock icon) and the keys do nothing.

1. Press and hold Stop/Clear (on some models Start) for four seconds until the lock clears.

The lock turns off and the panel answers again.