Chassis, generic

C05BE Brake Booster Motor B Position Sensor Supply Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C05BE is stored when the 5 V feed of motor B's position sensor exceeds its upper limit. No manufacturer documents it publicly. Two mechanisms are typical: the supply line has contacted a wire carrying battery voltage, or the reference ground of the sensor side has lifted, which makes every voltage measured against it look too high. Denso's patent illustrates the ground effect for a sensor read through a pull-down: a broken ground drives the signal above 4.7 V. In Hitachi Astemo's cross-check a rising ground pulls both references down while the monitor values stay put, which separates a ground fault from a true overvoltage. TI's tracker cuts its output path when shorted to battery. The booster then drops channel B and runs with motor A or reduced assist.

Likely causes

Motor B sensor supply shorted to a battery-voltage wire
Open or high-resistance sensor ground raising the measured voltage
Second sensor supply regulator out of regulation

Symptoms

  • Brake warning lamp and assist warning
  • Possibly further sensor codes if a shared ground is affected

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

C05BCC05BDC05BFC05BAC058D

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