Mercedes-Benz
Relay Actuation Without Stable Pilot Signal
Wallbox clicks (relay sound) but charging does not start; vehicle repeatedly connects and disconnects.
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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
Weak or unstable CP signal from Mercedes-Benz wallbox, Faulty power contactor not latching, Loose internal low-voltage connector to relay driver, Vehicle rejecting handshake due to timing issues
How to Fix / Troubleshooting
Safety first: Isolate power before touching internal components.
- Listen to sequence: Note whether the relay clicks once or repeatedly. Rapid clicking suggests unstable control signals.
- Inspect relay connections: With the cover removed, check that the control wires to the power contactor are firmly seated and not damaged.
- Check control board mounting: Ensure the control board is securely mounted and not flexing, which can stress solder joints.
- Test with another vehicle: If the behavior changes with a different EV, the issue may be vehicle-side.
- Service required: Persistent relay chatter usually indicates a control board or relay driver fault that requires professional replacement.
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Repair Difficulty
Hard
4/5
Required Part
Power Contactor / Relay Driver Circuit
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