E20
General Motors Load Sharing / Master‑Slave Communication Error

GM charger displays E20 and refuses to charge when connected through a GM‑branded load‑sharing or dual‑charger setup.

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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

Faulty RS‑485 or CAN communication link between GM chargers, Incorrect master/slave DIP switch settings, Damaged load‑sharing harness, Firmware mismatch between paired chargers

How to Fix / Troubleshooting

Safety first: Turn OFF breakers to all linked chargers before changing wiring or settings.

Steps:

  • Verify roles: Check DIP switches or configuration in each GM charger to ensure one is set as master and the others as slaves, per GM documentation.
  • Inspect communication cable: Examine the GM load‑sharing harness for cuts, kinks, or loose connectors. Reseat connectors firmly.
  • Update firmware: Ensure all linked chargers are running the same firmware version.
  • Test individually: Temporarily disconnect the communication harness and test each charger alone. If they work individually but not together, the issue is in the load‑sharing link.

Persistent E20 with correct wiring and configuration suggests a failed communication interface on one of the chargers. Replacement of the affected unit or its communication board is required.

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Repair Difficulty

Hard 4/5

Required Part

GM Load‑Sharing Communication Harness / Interface
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