Network, generic

U0343 Software Incompatibility With Hybrid/EV Battery Interface Control Module J

Check engine lightUsually off
EmissionsRelevant
Drive cycleNot required
Limp modePossible

J, the tenth board, only appears on larger packs. BMW's i8 is a documented example with more than ten: the parts list in bulletin SI B61 02 16 counts twelve cell monitoring circuits, and the battery electronics SME carries a voltage plausibility code for each of them, numbered 1 to 12 (21F0F3 to 21F0FE). The bulletin's cause is a failed CAN link between one or more CSCs and the SME, after which the contactor in the battery opens and the car cannot be made ready. BMW numbers the boards itself and does not use U0343; whether any maker maps J onto a tenth board in this way is not published. CARB asks for codes down to the smallest unit replaceable in service. U01A9 and U04AA are J's partners.

Likely causes

Tenth board carries software the battery controller does not accept
Replacement boards from different production batches combined
Internal battery bus disturbs the identification of board J

Symptoms

  • Car will not become ready to drive
  • High-voltage system switches off, contactor opens
  • Drivetrain malfunction message

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€100–1,500
Time1–5 h

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

Parts involved

hv battery interface module j

Related codes

U01A9U04AAU0342U0344

References: static.nhtsa.gov, law.cornell.edu.