On-Board Charger Faults
The AC charging path, its handshake, and why AC charging can fail while DC fast charging still works.
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Safety notice
- The on-board charger connects to the high-voltage battery. HV qualification and the manufacturer procedure are required.
What you will learn
- Describe the AC charging path
- Explain the charge handshake
- Diagnose a no-AC-charge complaint
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The on-board charger (OBC) takes AC from the charge port and converts it to DC to charge the traction battery, working with the BMS to control the current. Before any power flows, the vehicle and the charging station complete a communication handshake through the charge port.
A common complaint is “it will not charge at home but fast charging works”. That points at the AC path: the port, the pilot/communication pins, the OBC or the BMS request — not at the DC charging path used by a public fast charger.
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Key points
- Handshake first, power second.
- AC charging faults do not always stop DC charging.
- Inspect the port and communication pins before the OBC.
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Key points
- The OBC converts AC grid power to DC
- Communication precedes power
- AC and DC charging use different paths
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.
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