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Error code reference

Fisher & Paykel Dishwasher Error Code U4

Indicates that the F9 fault on the other tub of a double product means this tub cannot operate

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Indicates that the F9 fault on the other tub of a double product means this tub cannot operate. Do NOT replace the controller with the U4 fault.

First step from the service manual

Address the F9 fault on the other tub first.

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

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What U4 means on a Fisher & Paykel dishwasher

The U4 error code on a Fisher & Paykel double-drawer dishwasher is not a standalone fault. It is a communication-based status code that appears on one tub to indicate that the adjacent tub is experiencing an F9 fault. In a double dishwasher configuration, both tubs share system-level communication, and when one tub develops the F9 fault, it effectively prevents the other tub from operating. The U4 code is essentially a lockout notification, not a fault originating in the tub displaying it.

The F9 fault on the affected tub is the root cause that must be diagnosed and resolved first. Common causes of F9 include issues with the water inlet, drainage, or motor circuit on that tub. Because U4 is a downstream consequence of the F9 condition next door, performing any diagnostic work on the U4 tub itself will not resolve the problem. Replacing the controller on the tub showing U4 is explicitly not the correct repair path and will not clear the error.

Once the F9 fault on the originating tub has been properly diagnosed and corrected, the U4 code on the secondary tub should clear automatically. Technicians should focus all initial diagnostic attention on identifying and repairing the F9 condition. Only after the F9 is resolved should the U4 tub be re-evaluated if any error persists.

Source: manufacturer service documentation.

Common causes of U4

  1. 01

    Active F9 fault on the adjacent tub

    Wiring / connection

    The U4 code is directly caused by an unresolved F9 fault on the other tub in the double configuration. The F9 fault must be identified and repaired before the U4 tub can resume operation.

  2. 02

    Water inlet issue on the F9 tub

    Part replacement

    F9 faults can originate from a water supply problem on the affected tub, such as a blocked inlet valve or insufficient water pressure. Inspecting and resolving this condition on the F9 tub is part of clearing the U4 code.

  3. 03

    Drainage fault on the F9 tub

    Part replacement

    A drainage obstruction or pump failure on the F9 tub can trigger the F9 condition that causes the adjacent tub to display U4. Check the drain filter, drain hose, and pump on the F9 tub for blockages or failures.

  4. 04

    Motor or circulation fault on the F9 tub

    Part replacement

    If the F9 fault involves the wash motor or circulation system on that tub, the tub will go offline and cause the paired tub to show U4. Diagnosing the motor circuit on the F9 tub is required.

  5. 05

    Incorrect controller replacement on the U4 tub

    Wiring / connection

    Replacing the controller on the tub displaying U4 is a common misdiagnosis and will not resolve the issue. If a controller was already replaced on the U4 tub, the F9 fault on the other tub still needs to be addressed.

See the test procedure for each cause

Frequently asked questions about U4

What does U4 mean on a Fisher & Paykel dishwasher?
The U4 code appears on one tub of a Fisher & Paykel double-drawer dishwasher when the other tub is experiencing an F9 fault. It is a lockout notification, not an independent fault in the tub displaying it. The tub showing U4 cannot operate until the F9 condition on the adjacent tub is resolved. No repairs should be performed on the U4 tub until the F9 fault is addressed first.
How do I fix the U4 error on my Fisher & Paykel dishwasher?
To fix the U4 error, you must diagnose and repair the F9 fault on the other tub in your double dishwasher. The U4 tub itself does not require repair. Once the F9 fault is corrected, the U4 code should clear on its own. Do not attempt to replace the controller on the tub showing U4, as this will not resolve the issue.
Is it safe to use my Fisher & Paykel dishwasher when it shows a U4 error?
The tub displaying U4 is locked out and will not operate while the F9 fault exists on the adjacent tub. The U4 tub itself is not in a hazardous condition, but neither tub should be considered fully functional until the underlying F9 fault is diagnosed and repaired. Avoid repeated reset attempts and address the F9 fault directly.
Will resetting my dishwasher clear the U4 error code?
A simple reset will not permanently clear the U4 error because the code is caused by an active F9 fault on the paired tub. Even if the display clears temporarily after a reset, the U4 code will return as long as the F9 condition remains unresolved. The only way to permanently clear U4 is to diagnose and fix the F9 fault on the other tub.
How much does it cost to repair a U4 error on a Fisher & Paykel dishwasher?
The cost to resolve a U4 error depends entirely on what is causing the F9 fault on the adjacent tub. Repair costs can range from low-cost fixes like clearing a drain blockage to higher costs if components such as an inlet valve, drain pump, or wash motor need replacement. Parts and labor for those types of repairs typically range from $100 to $400 or more depending on the specific fault and local service rates.

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