E18
BMW Pre-Charge / Safety Relay Fault

BMW Wallbox shows E18; internal relay test failure, pre-charge or safety relay not operating correctly

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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

Stuck or welded pre-charge relay contacts, Failed relay coil, Faulty relay driver on control board, Wiring fault between relay and board

How to Fix / Troubleshooting

Safety first: This involves high-voltage components. Turn off the breaker and do not attempt to manually operate relays.

  • Power-cycle: After turning the breaker OFF for several minutes and then ON, see if the error clears temporarily.
  • Listen for relay clicks: During the start of a charging session, you should hear one or more relay clicks. Absence or continuous buzzing suggests a relay issue.

Because relay integrity is critical for safe operation, any persistent E18 requires professional service. A BMW-certified technician should test and replace the pre-charge/safety relay module or main board.

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Repair Difficulty

Professional Required 5/5

Required Part

BMW Wallbox Pre-Charge / Safety Relay Module
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