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U031B Software Incompatibility With DC/DC Converter Control Module A

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

DC/DC converter module A moves energy between two voltage levels, in hybrids and mild hybrids typically from the high-voltage or 48 V battery to the 12 V system. U031B means another module does not accept the converter's software. Audi documents it for the 2022-2023 A3, S3 and RS 3 with 48 V mild hybrid: after a 48 V battery replacement, battery management 2 (J1120) may store U031B00, because the updated battery (5WA.915.107.B) runs a validation check of voltage converter A7 that converter software 5WA.959.663 does not answer. With exactly these two part numbers Audi says the code can be ignored (TSB 2068368/1). On other combinations a genuine mismatch can stop the 12 V supply from being charged, so watch for battery or charging warnings. U0298 means lost contact. The MIL normally stays off.

Likely causes

48 V/HV battery or its management replaced by a newer version the converter software does not support
DC/DC converter replaced without programming or coding
Converter software behind the level of the other powertrain modules

Symptoms

  • Often no symptom, code found during service
  • 12 V battery or charging warning possible
  • Mild hybrid functions such as start-stop or recuperation limited

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€0–600
Time0.3–2 h

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

Parts involved

dc dc converter module acontrol module software

Related codes

U0298U0299U0312U0300

References: static.nhtsa.gov, en.wikipedia.org.