U04ACInvalid Data Received From Hybrid/EV Battery Interface Control Module L
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- High-voltage battery warning
- Power reduced, possibly no charging
- Likely causes
- PossibleInterface control module L faulty
- PossibleLoose plug on the internal link to module L
- RareFault at the pack's external low-voltage connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €150 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.