E09
Webasto
Phase Loss / Phase Sequence Error
Charger shows E09 or ‘phase error’; three-phase Webasto unit will not start or only charges at reduced power.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Missing phase at supply (blown fuse or breaker pole), Incorrect phase rotation (L1/L2/L3 swapped), Loose phase conductor in terminal block, Faulty phase detection circuit on PCB
How to Fix / Troubleshooting
Safety first: Only a qualified electrician should work on three-phase wiring.
- Check supply breakers/fuses: Verify all three phases feeding the Webasto charger are on and that no individual fuse has blown.
- Measure voltages: Have an electrician measure L1–L2, L2–L3, and L3–L1 at the charger input. All should be within the specified range and balanced.
- Verify phase order: For models that require a specific phase sequence, confirm L1, L2, and L3 are connected to the correct terminals as per the Webasto wiring diagram.
- Retighten terminals: With power off, retorque all phase conductors to the specified torque to eliminate loose connections.
- If wiring is correct: The internal phase detection circuit on the control board may be defective and require board replacement.
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Repair Difficulty
Professional Required
5/5
Required Part
Webasto Main Control PCB (Phase Detection Circuit)
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