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U04A1 Invalid Data Received From Hybrid/EV Battery Interface Control Module A

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U04A1 means the battery management controller keeps receiving messages from interface control module A, one of the slave boards that measure cell voltages and temperatures inside the high-voltage pack, but rejects their content as invalid. Volkswagen names the code: its on-car analysis list of 31 July 2024 for the ID.4 (2021–2024) files U04A1 together with U04A5 and U04A9 under the topic CMCe faults, stored in diagnostic address 8C, with an electrical system warning and no other relevant code there; dealers have to call the VW helpline before repairing. Silence from module A would be U01A0, a software mismatch U033A. Data errors of the battery energy control module itself are a separate code, U0412. Reduced power or no charging is possible until it is fixed.

Likely causes

Software issue in battery management or cell module controllers (VW ID.4 CMCe case, helpline first)
Interface control module A internally faulty
Loose or corroded connector on the pack-internal data link to module A
Weak 12 V battery disturbing the start-up of the battery electronics

Symptoms

  • Electrical system or high-voltage battery warning in the cluster
  • Reduced drive power
  • Charging interrupted or refused

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 a

Related codes

U01A0U033AU04A2U04A5U04A9U0412

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