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U01AB Lost Communication With Hybrid/EV Battery Interface Control Module L

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U01AB points at battery interface control module L, the twelfth position. The link to such a board has to bridge a large voltage offset, because the lowest and highest boards of a stack sit hundreds of volts apart. NXP's MC33771C, as one example, talks over a two-wire twisted pair coupled through transformers or capacitors at up to 2 Mbit/s, and Wikipedia's battery management article mentions optical isolation and radio as the alternatives. A broken coupling element or a damaged twisted pair at L can therefore cut the board off while it still measures correctly. No vehicle maker documents U01AB with a threshold of its own; GM lists it only in the 2018 fault bundle BICM Loss of Comm, so how the MIL behaves depends on the individual system.

Likely causes

Twisted-pair chain line to module L chafed, pinched or unplugged
Isolating transformer or capacitor on the link to L failed
Battery interface control module L defective

Symptoms

  • Battery or hybrid warning
  • Power limited, charging may be blocked

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–3,500
Time2–10 h

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

Parts involved

hv battery interface module lcommunication bus

Related codes

U01AAU01ACU04ACU0345

References: nxp.com, en.wikipedia.org, gsi.ext.gm.com.