Miele Dishwasher Error Code F91

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.

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.

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.

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.

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.