U04B1: Invalid Data Received From Battery Monitor Module
What to do
Expect stop-start to stop working, and possibly a battery warning, before anything else. The car has lost confidence in what it knows about its own battery, so it takes the cautious option.
The single most useful question: has the battery been replaced, and was the new one registered to the car? Many modern cars need to be told, and it takes a couple of minutes with the right tool. Skipping it causes this fault and also shortens the new battery's life, because the car keeps charging it as though it were the old one.
Mention anything wired directly to the battery — a dashcam, extra lights, an alarm or a tracker. Connected to the wrong post, they draw current the car cannot measure, and its accounting drifts until it stops making sense.
Have the battery and its terminals tested anyway. It is cheap, and a tired battery produces odd reports all over the car.
What this code means
The battery monitor is reporting a state of charge or health that cannot be accepted. See U0400 for the family's framing.
Modern cars measure their own battery far more carefully than most owners realise, and this code is a good place to explain why. A small sensor clamped around the negative terminal measures every amp entering and leaving the battery, its voltage and its temperature, and from those it keeps a running estimate of state of charge and of how much capacity the battery has lost with age.
That estimate drives real behaviour. The alternator is not simply switched on — charging voltage is chosen from what the battery needs, and deliberately reduced under acceleration to save fuel. Stop-start is permitted or refused on the same estimate. So is how long the car keeps its electronics awake after being locked.
Which gives this code its single most useful cause: a battery replaced without telling the car. The monitor keeps the ageing history of a battery that is no longer in the vehicle, so it reports a tired battery which now measures like a new one, and the numbers stop being consistent. On many vehicles registering the new battery is a two-minute procedure with a scan tool — and skipping it also causes a new battery to be undercharged into an early grave, which is why it matters beyond this code.
The second cause is anything wired around the sensor. A dashcam, winch, extra lighting or an alarm connected directly to the battery's negative post bypasses the measurement entirely, so current flows that the module cannot see and its arithmetic drifts.
The battery itself is still worth testing. A cell that has failed internally produces readings nothing can reconcile — and the corpus's standing note about supply faults applies: a marginal battery generates implausible reports across half the vehicle.
Likely causes
Start here
- New battery not registered to the vehicle · easy
- Low system voltage · easy
- Corroded or loose connector · easy
Less common
- Corroded earth connection · moderate
- Damaged wiring harness · 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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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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