U01ACLost Communication With Hybrid/EV Battery Interface Control Module M
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- U01AC belongs to battery interface control module M and is the last one GM mentions: its 2018 hybrid table ends the fault bundle BICM Loss of Comm at U01AC, i.e. thirteen boards, whereas GM's model-specific tables from 2016 to 2019 only monitor A to H. For diagnosis the order of events matters more than the letter. GM first sets the summary code U179C for one or more silent boards and only afterwards names the first board it cannot reach, so a workshop should record all stored module codes, U179C and the invalid-data and software codes of the same letter (U04AD, U0346) before clearing, then compare the count with the boards actually fitted. No manufacturer publishes a threshold or MIL type for M.
- What you may notice
- Summary code for missing boards stored together with U01AC
- Battery warning and reduced output
- Likely causes
- LikelyChain connection between module L and module M interrupted
- PossibleBattery interface control module M defective
- RareController calibration expects more boards than the pack contains
- 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: €100 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.