LG Dishwasher Error Code F-4

F-4 on an LG dishwasher means the microprocessor board detected a failure during startup and the dryer system is inoperative as a result. The board runs a self-check when the unit powers on, and when it finds an internal fault, it triggers F-4 and disables drying. This error points directly at the microprocessor board rather than a sensor or external component.

The dishwasher's wash cycle may still run with an F-4 error active, but the dryer will not function at all during this fault. Dishes will come out wet regardless of your drying settings. Continuing to use the unit long-term with an unresolved board fault is not advisable, as a failing microprocessor board can cause additional malfunctions over time.

A power reset, done by unplugging the unit or tripping the circuit breaker for one to two minutes, is worth attempting before any other steps. If the microprocessor board experienced a temporary initialization glitch, a reset may clear F-4. However, if the board has an actual hardware fault, the error will return on the next startup and a board replacement will be required.

LG's first troubleshooting step for F-4 is replacing the microprocessor board. Before ordering a board, check that all wiring harness connectors to the board are fully seated and undamaged, since a loose connection can mimic a board failure. If connections are secure and the error persists after a power reset, the microprocessor board will need to be replaced. A qualified appliance technician can confirm the diagnosis and perform the replacement if you are not comfortable working with control board components.

The microprocessor board for an LG dishwasher typically costs between $80 and $200 for the part, depending on the model. If you hire a technician, expect to add $100 to $200 in labor, bringing the total repair to roughly $180 to $400. DIY replacement is feasible if you are comfortable with appliance disassembly and handling circuit boards, as the board is generally accessible after removing the door panel.