P0A28: Hybrid/EV Battery Power Off Circuit Low
What to do
A car that will not power on with this code stored is applying a safety rule, not suffering a flat battery. Check the P0A27 service-plug story if any recent work applies; otherwise this needs a hybrid-qualified workshop, not home investigation.
What this code means
The battery power-off circuit reads low — shorted to ground, or open where the circuit's healthy state reads high.
Because this circuit exists to prove the disconnection chain is intact, the vehicle treats a bad reading conservatively: it may refuse to close the contactors at all, which presents as a car that will not enter READY. The causes are the family's usual ones — the service plug first if anyone has been near the battery, then connectors and wiring. See P0A27 for how the chain works.
Likely causes
Start here
- Wiring shorted to ground · moderate
- High voltage service plug not fully seated · easy
- 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
Be the first to write this up
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.
Sign in or create an account to add what you found about P0A28.