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U034B Software Incompatibility With Brake Booster Control

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Brake booster control is the electromechanical brake servo that replaces the vacuum booster and lets regenerative braking be blended in; in the VW group it is unit J539, which holds the pedal travel sensor and the motor position sensor (self-study 861213). Audi documents U034B00 on the 2025 A3 and S3: with servo software 0562 the unit logs U034B00 with symptom 500032 during the start phase, the engine controller adds P162400, a request to switch on the warning lamp, and the check engine light stays on. Audi blames the servo software, rules out part replacement and gives clearing the codes as the interim workaround (2076568/1); the booster keeps working. U025E is lost contact, U055F invalid data, and U031C names brake system control module B. Braking itself is unaffected.

Likely causes

Faulty software level in the electromechanical brake booster
Brake booster unit replaced without programming or coding
Brake or engine controller updated without matching the booster

Symptoms

  • Engine warning lamp stays on after starting
  • Request-MIL code stored in the engine controller
  • Code returns after clearing until new booster software is installed

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€0–600
Time0.3–1.5 h

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

Parts involved

brake booster module

Related codes

U025EU055FU031C

References: static.nhtsa.gov, static.nhtsa.gov.