Chassis, generic

C05C3 Brake Booster Motor A Supply Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Points to the power feed of booster motor A: fuse, supply cable, ground or the module input that carries battery current to the motor stage, rather than the motor windings themselves. No manufacturer documents C05C3 publicly. Bosch specifies its iBooster for supply voltages above 9.8 V with up to 450 W of motor power, so a weak feed shows up quickly under load. Hitachi describes cutting the booster motor current when the supply drops below or rises above set limits, and motor gate drivers such as the TI DRV8343-Q1 lock out on supply undervoltage. Check voltage drop on feed and ground while braking. Phase current faults are C0590/C0591, internal driver faults C0595, and the position sensor supply has its own codes.

Likely causes

Blown fuse or corroded high-current feed to the booster
Loose or corroded ground of the brake unit
Weak 12 V battery or charging fault causing voltage dips
Internal supply path of the brake module damaged

Symptoms

  • Brake warning lamp, loss or reduction of brake assist
  • Hard brake pedal, especially at low battery voltage
  • Further faults for regeneration or driver assistance braking

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€20–1,500
Time0.5–3 h

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

Parts involved

brake booster motor a supplyfuseelectric brake booster

Related codes

C05C2C0590C0591C0595

References: bosch-mobility.com, patents.google.com, ti.com, patents.google.com.