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U01A4 Lost Communication With Hybrid/EV Battery Interface Control Module E

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Chain link between module D and module E interrupted (open chain)
Module E itself defective (likely in ring designs when neighbours still report)
Return path of a ring layout damaged in addition to the main path

Symptoms

  • 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)

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–3,000
Time1–8 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

hv battery interface module ecommunication bus

Related codes

U01A3U01A5U04A5U033E

References: ti.com, patents.google.com, gsi.ext.gm.com.