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U01A2 Lost Communication With Hybrid/EV Battery Interface Control Module C

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U01A2 is stored when battery interface control module C, the third board of the chain, stays silent. How a controller reaches that verdict is spelled out in GM's 2016 hybrid table: the battery system module first logs U179C for one or more missing boards, then orders all boards into a loopback mode that bypasses the daisy chain. A board that answers in this mode still has power and working logic, so the master can separate a broken link from a dead unit and names only the first board it fails to recover; the code passes again once data returns for 100 ms. Audi bulletin 2081028 for the Q5 e (model years 2022 and 2024) lists U01A200 among the codes for modules A to H behind an electrical system malfunction warning.

Likely causes

Chain link between module B and module C broken (connector, ribbon, pin)
Module C fails the loopback test, board defective
Battery controller software that misreads the chain (update available)

Symptoms

  • Electrical system or hybrid warning in the instrument cluster
  • Reduced drive power or no electric driving
  • Code returns immediately after clearing

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 ccommunication bus

Related codes

U01A1U01A3U04A3U033C

References: gsi.ext.gm.com, static.nhtsa.gov, law.cornell.edu.