P0E3A: DC/DC Converter Voltage Sensor B Intermittent/Erratic
What to do
The car will usually drive. Watch for the twelve-volt battery going flat over the following days — that is this fault's real symptom, and replacing the battery will not fix it. If the car has been slow to wake or needed a jump start, say so.
What this code means
The circuit for one of the DC/DC converter's voltage sensors is faulty.
The DC/DC converter is the alternator's replacement, and the full argument for why that matters is at P0C38. In short: an electric car has no alternator, so every twelve-volt thing on it — lights, wipers, every control module — is fed by a converter stepping the traction pack down. When it stops, the twelve-volt battery is alone and the car dies within hours.
A converter has two voltage sides, and which one a sensor watches decides the entire diagnosis. The input side sees the traction pack at several hundred volts. The output side sees the twelve-volt system. A fault on the input is a battery or contactor problem; a fault on the output is a converter or twelve-volt problem, and they have nothing in common.
The standard does not say which of sensors A and B is which, and it varies by vehicle — the car's own documentation is the only authority. But the reading itself settles it in seconds: compare each sensor's live value against pack voltage and against the twelve-volt battery, and whichever it tracks is the side it watches. That is a free test worth doing before any part is ordered, because it decides which half of the car to work on.
Comes and goes. On a converter this often tracks load rather than time — it appears with the headlights and heated screen on and vanishes at idle — so a road test with everything switched on finds it where a static check will not.
Likely causes
Start here
- Faulty DC-DC converter · specialist
- Corroded or loose connector · specialist
- Open circuit in sensor wiring · specialist
Less common
- Damaged wiring harness · specialist
- Failed sensor reference voltage supply · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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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