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U033C Software Incompatibility With Hybrid/EV Battery Interface Control Module C

Check engine lightUsually off
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U033C names the third interface board. GM's closest published check is its own code P1EB1 in the VITM of the Volt: at power-up the controller compares its own software version with that of all slave boards and logs P1EB1 if any one does not fit, within 200 ms, with at least 9 V and no slave lost-communication fault active. The 2015 table enters it as one trip, the 2018 table as Type A, meaning a MIL after one failed drive. GM thus reports one summary code rather than one per board, and a letter code like U033C does not appear there. Where a maker does use the letter codes, C stands for the third board only; U01A2 covers lost contact with it, U04A3 invalid data.

Likely causes

Board C carries a software version the battery controller does not list as compatible
Battery controller updated while the boards stayed on the old level
Unstable low-voltage supply at power-up corrupts the version exchange

Symptoms

  • MIL possible on hybrids, as GM rates its comparable check Type A
  • Hybrid or high-voltage battery warning after switching on
  • Electric driving or charging restricted

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€60–800
Time0.5–2.5 h

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

Parts involved

hv battery interface module c

Related codes

U01A2U04A3U033BU033D

References: gsi.ext.gm.com, gsi.ext.gm.com.