Chassis, generic

C05BC Brake Booster Motor B Position Sensor Supply Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C05BC reports an interrupted supply for the position sensor of booster motor B. A B channel exists where the actuator carries a second motor or winding set, or measures its rotor angle twice for redundancy. No manufacturer documents C05BC publicly. Hyundai Mobis describes a brake actuator with a dual-winding motor whose two power modules are fed separately; when one is diagnosed faulty it is shut down and the full current command passes to the other. Hitachi Astemo pairs each sensor supply with its own angle and torque sensor and keeps the motor running on the healthy set. As in Denso's analysis, a broken feed drags the signal to 0 V. The usual result is a brake warning with reduced assist, while full failure of boosting is avoided.

Likely causes

Broken wire or pushed-back pin in the motor B sensor supply
Second sensor supply output in the control unit failed
Open inside the motor B position sensor

Symptoms

  • Brake warning lamp, assist may remain partly available
  • Reduced maximum assist or slower pressure build-up

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–3,000
Time1–4 h

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

Parts involved

booster motor b pos sensor supplyelectric brake booster

Related codes

C05BDC05BEC05BFC05B8C058B

References: patents.google.com, patents.google.com, patents.google.com.