Error code reference

LG Dishwasher Error Code F-4

Board failure on start up; dryer is inoperative.

LG codesLG dishwasher codes

Board failure on start up; dryer is inoperative.

First step from the service manual

Replace microprocessor board.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What F-4 means on a LG dishwasher

The F-4 error code on an LG dishwasher indicates a microprocessor board failure detected at startup, resulting in an inoperative dryer system. The control board runs a self-diagnostic check when the unit powers on, and when the microprocessor detects an internal fault or fails to initialize correctly, it throws F-4 and disables drying functionality. Because the dryer circuit depends on signals from the microprocessor board to operate heating elements and fan components, a compromised board means the drying cycle cannot execute regardless of the wash cycle status.

For homeowners, this means the dishwasher recognized a problem with its main brain, the microprocessor board, before it could even get started. The drying function, whether heated dry or fan-assisted, will not work while this error is active. The board essentially flagged itself as faulty during its startup check. You may still see lights or hear the unit respond, but drying will be completely disabled until the underlying board issue is resolved.

Because this error points directly to the microprocessor board rather than a sensor, wiring, or peripheral component, troubleshooting paths are limited. LG's first recommended action is replacing the microprocessor board, which is the component responsible for all cycle logic and output commands to the dryer system.

Source: manufacturer service documentation.

Common causes of F-4

  1. 01

    Failed microprocessor board

    Part replacement

    The microprocessor board itself has an internal fault, damaged circuitry, or a failed processor chip that prevents it from completing its startup sequence. This is the primary cause of F-4 and the reason LG directs technicians straight to board replacement.

  2. 02

    Power surge or voltage spike damage to the board

    Part replacement

    A sudden voltage spike from the home electrical supply can damage the microprocessor board's components without visibly burning or scorching the board. The damage may be internal to the processor or onboard capacitors, triggering the F-4 fault at every subsequent startup.

  3. 03

    Corrupted board firmware or failed boot sequence

    Part replacement

    In some cases the microprocessor board's firmware can become corrupted, preventing it from initializing correctly and triggering an F-4 at startup. This can occasionally result from a power interruption mid-cycle, though a board replacement is still typically required to resolve it.

  4. 04

    Loose or damaged wiring harness connection to the microprocessor board

    Wiring / connection

    A connector that has worked loose from the microprocessor board or a wire with compromised insulation can prevent the board from receiving stable power or communication signals, which may cause the board to fail its startup check and throw F-4.

See the test procedure for each cause

Frequently asked questions about F-4

What does the F-4 error code mean on an LG dishwasher?
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.
How do I fix the F-4 error code on my LG dishwasher?
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.
Can I still use my LG dishwasher when the F-4 error is showing?
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.
How much does it cost to fix an F-4 error on an LG dishwasher?
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.
Will resetting my LG dishwasher clear the F-4 error code?
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.

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