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U01B3 Lost Communication With Brake Blending Actuator

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The brake blending actuator divides each braking request between regeneration by the drive motor and the friction brakes, keeping pedal feel steady while the share shifts. Bosch states that its electromechanical iBooster, together with the ESP hev unit, can blend up to 0.3 g of deceleration. U01B3 is stored when the unit coordinating the brakes, normally the hybrid or brake controller, no longer hears this actuator. No manufacturer documents the code publicly. Lost recuperation raises energy use and, on hybrids, engine running time, and CARB 1968.2 expects hybrid systems to detect faults that disable regenerative braking. The friction brakes then do all the work: expect weaker recuperation, a changed pedal and a brake or hybrid warning. U04B4 is the invalid-data code.

Likely causes

CAN wiring or connector fault at the brake actuator
Actuator without supply voltage, often after low 12 V voltage
Brake blending actuator electronics faulty

Symptoms

  • Little or no regenerative braking
  • Changed brake pedal feel
  • Brake or hybrid system warning

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,800
Time1–4 h

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

Parts involved

brake blending actuatorcan bus

Related codes

U04B4U01B4U0129

References: bosch-mobility.com, en.wikipedia.org, law.cornell.edu.