E12
Mercedes-Benz
Phase Loss / Asymmetry Detection
Wallbox shows E12; charging power is lower than expected; vehicle may show reduced charging rate.
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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
One phase missing in three-phase supply, Blown upstream fuse on one phase, Loose phase conductor at wallbox terminal block, Internal relay failure on one phase in Mercedes-Benz wallbox
How to Fix / Troubleshooting
Safety first: Only a qualified person should work on three-phase circuits. Isolate power before opening the unit.
- Check upstream protection: Inspect the distribution board for a tripped or blown fuse on one of the phases feeding the wallbox. Reset or replace only after identifying the cause.
- Inspect terminal block: With power off, open the wallbox and verify that L1, L2, and L3 conductors are all present and firmly tightened.
- Measure phase voltages: An electrician should measure each phase-to-neutral and phase-to-phase voltage at the wallbox terminals to confirm all phases are present and balanced.
- Internal relay check: If supply is correct but E12 persists, one of the internal power relays may not be closing. This requires diagnostic testing and possible replacement of the power relay assembly.
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Repair Difficulty
Hard
4/5
Required Part
Three-Phase Power Relay Assembly
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