U04AC code meaning
Invalid Data Received From Hybrid/EV Battery Interface Control Module L
Network system Generic code U04xx codes Check engine light
What U04AC means
U04AC covers interface module L, the twelfth letter. Twelve is a common pack size: Wikipedia gives twelve modules for the larger ID.4 battery and for the Ultium pack of the Cadillac Lyriq. Where one board serves each module, L would be the last board present there. Whether a maker actually wires it that way is not public; the 2024 Volkswagen list names only A, E and I for that car, and no source names U04AC. The code means messages from L arrive but fail the controller's checks, not that L has gone quiet (U01AB) or carries the wrong software (U0345). Tracing it requires the manufacturer's scan tool and, beyond the external low-voltage connections, work on an opened high-voltage battery.
U04AC at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor1.5 to 10 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U04AC
- High-voltage battery warning
- Power reduced, possibly no charging
Common causes of U04AC
- PossibleInterface control module L faulty
- PossibleLoose plug on the internal link to module L
- Less likelyFault at the pack's external low-voltage connector
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hv battery interface module l
What each part of U04AC means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| AC | The exact fault in that area. |
What to do next
- Note U04AC 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 U04AC
What does U04AC mean?
U04AC means "Invalid Data Received From Hybrid/EV Battery Interface Control Module L". U04AC covers interface module L, the twelfth letter. It is a generic code, so it means the same on every make.
Is it safe to drive with U04AC?
Drive gently and only to a workshop. With U04AC the car can go into limp mode (reduced power) to protect itself.
Will U04AC fail an emissions test?
Yes, it can. U04AC 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 U04AC to fix?
Difficulty: workshop only. A typical repair takes 1.5 to 10 hours of work. This is a job for a workshop.
Will U04AC clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.