U04B1 code meaning
Invalid Data Received From Battery Monitor Module
Network system Generic code U04xx codes Check engine light
What U04B1 means
Despite its place after the high-voltage interface series, U04B1 usually concerns the 12 V side: in GM's 2024 OBD table 24OBDG07 the battery monitor module is the intelligent battery sensor on the 12 V battery, read by the body control module over LIN. GM sets U04B1 when the alive rolling counts of the sensor's signals, among them charged and discharged amp-hours, state of charge, temperature and crank data, are wrong in 8 of 10 samples, polled every 250 ms, with the car in run, above 11 V and at least 5 s after power-up; Type B, two trips. Alfa Romeo reported U04B1-00 in the PCM of 2017–2019 Giulia and Stelvio after a module flash and cleared it with a BCM configuration restore. U01B0 means the sensor is silent.
U04B1 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.3 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U04B1
- Check engine light (GM Type B, after two trips)
- Start-stop disabled or charging strategy of the generator changed
Common causes of U04B1
- Most likelyBody control module configuration lost or mismatched after reprogramming (Alfa Romeo)
- PossibleIntelligent battery sensor on the negative terminal faulty
- PossibleLIN lead or plug at the battery sensor damaged or corroded
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Battery monitor module
What each part of U04B1 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| B1 | The exact fault in that area. |
What to do next
- Note U04B1 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U04B1
What does U04B1 mean?
U04B1 means "Invalid Data Received From Battery Monitor Module". Despite its place after the high-voltage interface series, U04B1 usually concerns the 12 V side: in GM's 2024 OBD table 24OBDG07 the battery monitor module is the intelligent battery sensor on the 12 V battery, read by the body control module over LIN. It is a generic code, so it means the same on every make.
Is it safe to drive with U04B1?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U04B1 fail an emissions test?
Yes, it can. U04B1 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U04B1 to fix?
Difficulty: medium. A typical repair takes 0.3 to 1.5 hours of work. This is a job for a workshop.
Will U04B1 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.