P0A08: DC/DC Converter Status Circuit
What to do
If the twelve-volt battery keeps going flat, be aware there is no alternator on this car to blame — the DC-DC converter does that job, and this code concerns it. And if the car seems completely dead, that is usually the small twelve-volt battery rather than the main pack: it is the thing that wakes everything else, and the main pack is unreachable without it.
What this code means
A fault in the circuit reporting the status of the DC-DC converter. Understanding what this part does explains one of the most misread situations on any hybrid.
A hybrid has no alternator. The twelve-volt system — lights, wipers, radio, the computers themselves — is supplied by the DC-DC converter, which steps the high-voltage pack's several hundred volts down to the fourteen or so a conventional electrical system expects. It does the alternator's job by entirely different means.
So a hybrid with a flat twelve-volt battery and no obvious charging is not an alternator fault, because there is nothing to replace. It is this converter, its control, or the signal reported here.
The second consequence surprises people more. A hybrid with a fully charged high-voltage pack and a flat twelve-volt battery will do nothing at all. The small battery is what wakes the computers, closes the high-voltage contactors and lets the car reach its ready state; without it the several hundred volts sitting in the pack are unreachable. A hybrid that is completely dead on the driveway very often needs nothing more than its small battery attended to.
Likely causes
Start here
- Faulty DC-DC converter · specialist
- Corroded or loose connector · easy
- Failing 12 volt battery · easy
Less common
- Open circuit in status wiring · moderate
- Poor module ground connection · moderate
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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