Miele Washer Error Code F4129

F4129 is a tachogenerator connection fault that triggers at program end when the control board detects no tachogenerator signal after the safety time has elapsed. The tachogenerator is a small generator mounted on the drive motor that produces an AC frequency signal proportional to motor speed. This signal is continuously monitored by the frequency converter to verify that the motor is spinning at the correct speed. When the signal is absent at the end of a wash cycle, the control system logs F4129 to indicate that the motor speed feedback loop was broken or never established during that final phase of operation.

The most critical initial focus should be on the tachogenerator's wiring harness and its connection to the frequency converter relay K1/9. Loose connector pins, broken wires, or corroded terminals between the tachogenerator and the relay can interrupt the signal path entirely. The frequency converter relay K1/9 is the interface component that processes the incoming tachogenerator frequency and relays motor performance data back to the main control board. A fault at this relay, whether due to a failed relay coil, damaged PCB traces, or poor solder joints, can produce the same symptom as a completely dead tachogenerator.

Beyond wiring and relay issues, the tachogenerator itself can fail internally. The small generator coil can develop an open circuit, or the magnetic coupling between the generator and the motor shaft can degrade, resulting in a weak or absent output signal. In some cases the motor itself may have stalled or experienced a bearing failure that prevented it from reaching a detectable speed, which would also cause no signal to be generated.