P0D20: Battery Charger A Output Voltage Performance
What to do
The car will usually still drive. It may charge slowly, stop part way, or refuse to start a charge at all. Try a different charge point before assuming the car is at fault — this code can be the honest reporting of a poor supply. The charger itself is a high-voltage assembly and is not a home repair.
What this code means
The on-board charger's high voltage output is not at the voltage it was commanded to produce.
The on-board charger is a separate device from everything else in this part of the car, and confusing it with its neighbours is the commonest way this family gets misdiagnosed. It is not the DC/DC converter — that one steps the traction pack down to run the 12-volt system, and lives at P0C38 and P0D32. It is not the pack itself. The on-board charger takes mains alternating current from the wall and turns it into direct current at the several hundred volts the traction battery wants. It only runs while the car is plugged in, which is why every fault in this family is invisible on a road test.
A charger works in two modes, and which one it is in decides which test is running. Early in a charge it holds a constant current and lets the voltage climb; near the top it holds a constant voltage and lets the current taper. This code is the constant-voltage half: the battery management system asked for a particular voltage, the charger acknowledged it, and the voltage measured on the output is not that.
It is a performance code rather than a circuit code, which means the charger is alive. It is producing something. So the useful order of investigation is outward rather than inward: what is arriving on the input side (P0D27-P0D2A), whether the charger is derating itself for heat (P0D24), and whether the sensor reporting the output is telling the truth (P0D4C) — before anybody condemns a unit that is one of the most expensive parts on the car.
Likely causes
Start here
- Faulty on-board charger · specialist
- Fault in the external charging equipment · easy
- Corroded or loose connector · specialist
Less common
- Faulty battery pack sensor module · specialist
- Damaged wiring harness · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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