Wallbox shows E03 and refuses to start charging; status LED may flash red/orange; vehicle may show ‘Ground fault’ or ‘Charging station error’.

Safety first: Switch off the wallbox circuit breaker and any upstream RCD/RCBO. Do not attempt to bypass safety devices.

• Visual inspection for moisture: Open the wallbox housing per the service instructions. Look for condensation, water tracks, or corrosion around the RCD sensor module and control board. If moisture is present, the unit must be dried and the source of ingress (gasket, cable gland) corrected.
• Check cable glands and seals: Ensure all cable entries are tight and rubber grommets are seated correctly. Replace damaged gaskets or glands.
• Drying procedure: If minor moisture is found, disconnect power, remove the unit cover, and allow the interior to dry in a warm, dry environment for 24 hours. Do not use open flame or excessive heat.
• Test with another vehicle: After drying and reassembly, restore power and test with a different EV if possible. If E03 only occurs with one vehicle, the vehicle’s onboard charger may be leaking DC current and should be inspected by a dealer.
• Technician required: If E03 persists with multiple vehicles and no moisture is present, the internal DC RCD sensor or associated electronics are likely defective. Replacement of the RCD module or control board must be performed by an authorized Mercedes-Benz wallbox service provider.