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U01A6 Lost Communication With Hybrid/EV Battery Interface Control Module G

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U01A6 means battery interface control module G no longer reports to the battery controller. Because these boards sit inside the high-voltage pack, the chain runs between modules whose ground levels differ by hundreds of volts, so the link has to be galvanically isolated; Wikipedia's battery management article names optical couplers and radio as the hardware routes. Diagnosis therefore starts on a de-energised pack: note which neighbouring letters still report, then look at G's plugs for corrosion, coolant or moisture and carry out an insulation test before swapping parts. GM's 2016-2019 plug-in tables classify G as Type A, lighting the MIL in the first failing trip, and Audi's bulletins for the 2016 A3 e-tron and the Q5 e list U01A600 together with the other seven letters.

Likely causes

Chain link between module F and module G interrupted
Moisture or coolant at the chain connectors of module G
Isolating coupler (transformer, optocoupler) on the link to G failed
Battery interface control module G defective

Symptoms

  • MIL and battery warning lamp
  • Insulation fault code stored alongside if moisture has entered
  • Reduced power or no ready mode

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 gcommunication bus

Related codes

U01A5U01A7U04A7U0340

References: en.wikipedia.org, gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.