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U01A9 Lost Communication With Hybrid/EV Battery Interface Control Module J

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U01A9 stands for battery interface control module J, the tenth board. Apart from wiring, a typical trigger after repairs is configuration: monitoring chips in a chain usually get their address when communication starts. NXP's MC33771C cell controller, for instance, receives its address during initialisation and supports up to 63 nodes per chain, and a Nuvoton patent (US20210184474) describes addresses handed out one after another at start-up in daisy-chained supervisors. A replaced or reordered board that fails to take its slot may therefore go missing for the master. Software mismatch with the same board has its own code, U0342. No manufacturer documents U01A9 with a monitor of its own; GM only lists it in the 2018 bundle BICM Loss of Comm.

Likely causes

Chain connection between module I and module J interrupted
Board J not addressed or registered after module replacement
Battery interface control module J defective

Symptoms

  • Code appears right after battery repair or module replacement
  • Vehicle not ready to drive or power limited

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€0–3,000
Time0.5–8 h

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

Parts involved

hv battery interface module jcommunication bus

Related codes

U01A8U01AAU04AAU0343

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