P0B25: Hybrid/EV Battery A Voltage Low
What to do
Ask what the voltage does after a full charge — that one question separates "it was discharged" from "it no longer holds charge", and they have very different bills. If the vehicle has stood unused for a long period, say so; deep discharge from long-term parking is a known and sometimes recoverable cause. Do not attempt to charge or jump a high-voltage pack by any improvised means.
What this code means
Battery A's voltage is below what the module expects.
Low has an ordinary explanation and an unwelcome one, and they are separated by when the reading is low. A battery that is low because it is discharged recovers when it is charged. A battery that is low regardless of charging has lost capacity — cells that no longer hold what they held, or a section that has failed and is dragging the string down.
The distinction is easy to make and is the first thing worth asking for: what does the voltage do after a full charge? If it comes up and stays up, the fault is in charging or in whatever discharged it. If it does not, the battery itself is the answer.
A third possibility should be ruled out before either: the reading may simply be wrong. P0B14's argument about measurement is directly relevant here, and a section reading low because its measuring wire has gone high-resistance is indistinguishable from one that is genuinely flat.
Likely causes
Start here
- Hybrid battery pack deterioration · specialist
- Weak or failed cell group in the battery pack · specialist
Less common
- Deeply discharged after long-term parking · moderate
- Damaged cell voltage sense harness · specialist
- Corroded or loose connector · easy
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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Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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