P0B28: Hybrid/EV Battery B Voltage Unstable
What to do
As P0B24 — connections before batteries, because voltage that steps with demand is describing a joint rather than a cell.
What this code means
Battery B's voltage is moving in ways its load does not explain — the resistive-joint signature set out at P0B24, where the cheap answer is genuinely the likely one.
Likely causes
Start here
- Corroded or loose connector · easy
- Corroded battery terminals · easy
Less common
- Weak or failed cell group in the battery pack · specialist
- Faulty battery contactor · 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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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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