BMW Wallbox shows E20; internal isolation fault between control and power circuits

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.

Possible Causes

Failed isolation transformer in power supply, Breakdown of optocouplers between logic and power stage, Moisture or contamination bridging isolation gaps, Surge damage

How to Fix / Troubleshooting

Safety first: This is a serious internal electrical fault. Immediately turn off the breaker and do not use the Wallbox.

Do not open the unit: Isolation faults require specialized testing and are not user-serviceable.
Arrange service: Contact a BMW-authorized service partner for inspection and likely replacement of the main power module or entire Wallbox.

Do not attempt to bypass or ignore E20; doing so could create a shock hazard.

Repair Difficulty

Professional Required 5/5

Required Part

BMW Wallbox Isolated Power Module / Main Control Board

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