U01A4Lost Communication With Hybrid/EV Battery Interface Control Module E
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- U01A4 concerns battery interface control module E. Whether such a code points to one board or to a whole broken chain depends on the wiring scheme. In a plain daisy chain a break silences all boards behind it, and GM's logic names only the first. Some monitoring chips allow a closed ring instead: TI's BQ79616 offers an isolated differential daisy chain with an optional ring, and a CATL patent (US11031789) describes a controller that, after the loop breaks, drives the two remaining halves through its two serial ports. In such designs a lone E code is much more telling, since boards beyond the gap are still heard from the far end. GM's eight-board plug-in tables of 2016-2019 rate the loss of E as Type A.
- What you may notice
- Battery warning and reduced output
- Only module E reported missing although later boards are silent too (open chain)
- MIL on the first trip (GM Type A)
- Likely causes
- LikelyChain link between module D and module E interrupted (open chain)
- PossibleModule E itself defective (likely in ring designs when neighbours still report)
- RareReturn path of a ring layout damaged in addition to the main path
- 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 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.