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U04B4 Invalid Data Received From Brake Blending Actuator

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

In hybrid and electric cars, brake blending decides how much of the requested deceleration the drive motor recovers as energy and how much the friction brakes supply; at low speed the hydraulic brakes take over completely. An electromechanical booster such as Bosch's iBooster, paired with a matching ESP, is rated for blending up to about 0.3 g of regenerative deceleration. U04B4 is stored when messages from the blending actuator arrive but their values are not credible. No manufacturer documents this code publicly. CARB 1968.2 requires hybrids to flag faults that disable or degrade regenerative braking, so a MIL is possible. U01B3 marks a silent actuator. Expect less regeneration, a changed pedal feel and a brake warning.

Likely causes

Blending actuator or its pedal/position sensing faulty
Chassis bus wiring or connector fault
Brake and drive controller software not matching after update or replacement
Low 12 V supply affecting the actuator electronics

Symptoms

  • Brake system or hybrid warning light on
  • Little or no regenerative braking, shorter range
  • Brake pedal feels different or harder

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–2,000
Time0.5–3 h

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

Parts involved

brake blending actuator

Related codes

U01B3U04B5

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