Diagnosis
The display showing 'FP' indicates a firmware process is active or stuck. This commonly happens after a power interruption during an update or a failed internal boot sequence.
How to Fix It
Perform a full factory reset. Disconnect the soundbar and subwoofer from power. Wait two full minutes. Reconnect the power cord to the soundbar only. Use a paperclip to press and hold the small reset pinhole on the back for 10 seconds. The unit will power cycle and the display should clear.
If That Didn't Work
A sustained 'FP' indicates a corrupted main board firmware. The fix requires a manual USB update. Download the latest firmware for model S40Q directly from the LG support site. Extract the .bin file to a USB drive, plug it into the soundbar's service port, then power on. The update process will start automatically.
Heads Up
The subwoofer must be re-paired after a factory reset. After the soundbar resets, power on the subwoofer. Press and hold the 'PAIRING' button on the back of the subwoofer for 5 seconds until its LED blinks rapidly. The soundbar will automatically search and connect.