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Error code reference

Miele Dishwasher Error Code F91

Load size registration inactive; water intake block operates with default water quantity instead of…

Miele codesMiele dishwasher codes

Load size registration inactive; water intake block operates with default water quantity instead of load-dependent quantity. Only indicated in fault memory.

First step from the service manual

Replace the speed sensor.

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

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What F91 means on a Miele dishwasher

The F91 fault code on a Miele dishwasher indicates that the load size registration system has become inactive. Under normal operation, Miele dishwashers use a speed sensor to detect the volume of dishes loaded into the machine. This data allows the water intake block to calculate and deliver a precise, load-dependent quantity of water for each cycle, optimizing water and energy consumption based on actual load volume. When F91 is triggered, this adaptive intake function is disabled and the control system falls back to a fixed default water quantity for every cycle regardless of how full or empty the machine is.

The primary component involved in this fault is the speed sensor, which feeds load-size data to the control board so the water intake block can make real-time adjustments. A failed, disconnected, or out-of-specification speed sensor breaks this feedback loop entirely. The control board detects the missing or invalid signal and logs F91 in the fault memory, then defaults to a preset water volume to allow the machine to continue operating. Importantly, this code does not cause an immediate cycle stoppage and will not display on the control panel during normal use. It is only visible when the fault memory is accessed during a diagnostic or service read-out.

Because the machine continues to run using the default water quantity, many users will not notice any obvious performance change, though water usage may be slightly higher or lower than optimized levels depending on typical load sizes. The recommended first diagnostic action is replacement of the speed sensor, as this component is the most direct cause of the registration failure.

Source: manufacturer service documentation.

Common causes of F91

  1. 01

    Failed speed sensor

    Part replacement

    The speed sensor is the primary component responsible for load size detection. A failed sensor sends no signal or an invalid signal to the control board, directly triggering the F91 code. Replacement of the speed sensor is the first recommended diagnostic step.

  2. 02

    Speed sensor wiring or connector fault

    Wiring / connection

    Damaged wiring, a loose connector, or corrosion between the speed sensor and the control board can interrupt the signal without the sensor itself being defective. Inspect the harness and connectors for visible damage, moisture intrusion, or poor seating.

  3. 03

    Speed sensor mounting or positioning issue

    Wiring / connection

    If the speed sensor is not correctly seated or has shifted out of its mounting position, it may fail to register correctly even if electrically intact. Check that the sensor is properly secured and aligned according to its mounting specification.

  4. 04

    Control board fault

    Part replacement

    In cases where the speed sensor and its wiring check out correctly, the control board may not be processing the sensor signal properly. A control board fault is a less common cause but should be considered after ruling out the sensor and wiring.

See the test procedure for each cause

Frequently asked questions about F91

What does F91 mean on a Miele dishwasher?
F91 means the load size registration system is inactive. Normally, Miele dishwashers use a speed sensor to detect how much is loaded and adjust the water intake accordingly. When this sensor fails or loses signal, the machine logs F91 in the fault memory and switches to a fixed default water volume. The dishwasher will continue to operate, but water usage is no longer optimized to the actual load size.
How do I fix the F91 fault code on my Miele dishwasher?
The recommended first step is to replace the speed sensor, as it is the most common cause of the F91 code. Before replacing the sensor, also inspect the sensor wiring harness and connectors for any damage, corrosion, or loose connections. If the sensor and wiring are found to be intact, the control board should be evaluated as a secondary cause. A qualified technician can access the fault memory and test the sensor circuit to confirm the root cause before parts are ordered.
Is it safe to keep using my Miele dishwasher with an F91 code?
Yes, the F91 code does not indicate a safety hazard or a condition that stops the machine from running. The dishwasher will continue to complete wash cycles using a default water quantity. However, water consumption will not be optimized for your actual load size, and the underlying fault should be repaired to restore full efficiency. Continuing to run the machine without repair is low risk but not ideal for long-term performance.
Will resetting my Miele dishwasher clear the F91 code?
A basic reset may clear the F91 code from the active display, but the code will return to the fault memory if the underlying cause is not repaired. F91 is stored in the fault memory and is only visible during a diagnostic read-out, so it may not reappear visibly even if the fault is still present. Proper resolution requires diagnosing and correcting the speed sensor or wiring issue rather than relying on a reset.
How much does it cost to repair an F91 fault on a Miele dishwasher?
Repair costs vary depending on whether the fix requires only a wiring correction or a full part replacement. A new speed sensor typically falls in the range of $30 to $80 for the part alone. If a technician is needed for diagnosis and installation, total repair costs including labor commonly range from $100 to $250. Control board replacement, if required, would increase the cost significantly.

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